Watson's Biblical & Theological Dictionary 
a sect so called from Faustus Socinus, who died in Poland in 1604. This celebrated man was born in Tuscany, and was descended from an ancient and noble family. In the earlier period of his life he devoted little time to literary acquisitions, but he was possessed of a vigorous understanding, and of that steady fortitude which qualified him for the memorable part which he afterward acted. His connection with his uncle Laelius probably gave a bias to his mind with respect to religion. He warmly embraced his tenets, and he spent a great part of his days in studying and disseminating them. Having left his native country, he visited Poland; and finally he settled in it for the express purpose of propagating his own peculiar views of religious truth. The fundamental principles which he assumed were, the rejection of all mystery from revelation, and the necessity of trying its doctrines by the light of reason; and he rigorously applied this latter maxim in conducting has theological investigations. He inculcated in the strictest sense, the unity of God; considered the Word and the Holy Ghost as attributes of the supreme Being; taught that Christ was a man peculiarly honoured by the Almighty, having been born through the operation of the Spirit; and that he was so highly exalted, in consequence of his office as the Saviour of the world, that he might be styled the Son of God, and ought to be worshipped. Struck with several declarations of our Lord which seemed to imply that he had descended from heaven, and which militated against his leading tenet respecting Jesus, he endeavoured to evade the application of them, by supposing or affirming that, previous to the commencement of our Saviour's ministry, he had, through the power of God, been taken up to the celestial regions, and had in them received from the Almighty the truths which he was commissioned to reveal.
The first reception of Socinus in Poland, even by those who might have been expected to welcome him, was most discouraging. The Unitarian churches which had been previously established in that kingdom, differing from him in several points, would not admit him into their communion; and he had to encounter the enmity of the great majority of Christians, who abhorred his tenets, and branded them as impious. But, notwithstanding all this, and although he was visited with much suffering and affliction, his perseverance, his talents, and his zeal soon excited admiration; his views were adopted by many even in the highest stations of life; his principles were embodied in a catechism, which, though not imposed upon his followers, they read with very extensive acquiescence; and he had the satisfaction of beholding the sentiments which he had long cherished, embraced by various churches enjoying the protection of government, and permitted to establish seminaries of education by which the impression made on the public mind might be preserved and deepened. There was not, however, perfect unanimity of faith among all his associates who united in denying the divinity of our Lord. Vast numbers of these, previous to their having perused the papers of Laelius Socinus, had so far received the system of Arianism, that they believed Christ to have existed before he entered into the world; and although many, in consequence of the reasonings and representations of Socinus, abandoned this doctrine, it was retained by some, who, from their leader, were called Farnovians. Socinus conducted himself toward these men with admirable address. Fully aware that the tendency of their having departed so far from the orthodox tenets was to lead them to still farther recession, and sensible that his own system naturally and consequentially resulted from what they readily admitted, he used every method to conciliate them, and he permitted them to remain with his followers, upon condition of their not openly insisting on the preexistence of Christ. They did, however, at length separate from the great body of his adherents; but they gradually approached nearer and nearer to them, and, upon the death of Farnovius, most of them incorporated themselves with the Socinians, and all trace of them as a distinct party was obliterated.
Socinus was much more agitated by the promulgation of an opinion very opposite to those now mentioned. As might have been anticipated, there were some who, having adopted the sentiments of Laelius Socinus as to the simple humanity of Christ, deduced from this tenet consequences which appeared to them obviously to flow from it, although these had not been perceived or admitted by Laelius himself. A striking example of this took place in the time of Faustus Socinus. Francis David, a man of considerable influence among the Unitarians, being the superintendent of their churches in Transylvania, maintained that, as Christ was born just like other men, so he continued, notwithstanding his exaltation, to be merely a human being; and that therefore all invocation of him, and worship paid to him, were to be shunned as impiety or idolatry. Socinus inveighed with the utmost warmth against this opinion; he used every method to induce David to renounce it; and, at the desire of one of his friends, he resided for a considerable time at the house of his opponent, that the subject at issue might be fully and calmly discussed. He failed, however, in accomplishing his object. David persisted, as he had, upon the ground which he had taken, good reason to do, in asserting the doctrine which he had announced; and he was soon after this thrown by the prince of Transylvania into prison, where he lingered for several years, and then died at an advanced age. It has been insinuated that Socinus was accessary to this cruel deed of detestable persecution; and, although attempts have been made to wipe off the imputation, there is too much cause to think that it is not wholly unfounded. Most certain it is, that he had it much at heart to root out what he viewed as the heresy of David, and that the support of it after the death of the unhappy sufferer by some distinguished Unitarians gave him much uneasiness. It is not unlikely that the zeal which he thus displayed arose from his apprehension that the tenets which he opposed would supplant his own, and from the difficulty that he must have experienced in turning aside the inferences which were affirmed to follow from what he admitted. If such was the case, and it seems in many respects more probable than the conjecture of Mosheim, that it is to be attributed to the dread of rendering the sect more odious than it actually was, we have a striking proof of his discernment, though at the expense of his candour; for the present creed of Unitarianism approaches much nearer to that of David than to the doctrines of the founder of Socinianism himself.
But, while he was thus disquieted by opposition which, after the liberty with which he had himself departed from the faith of the most ancient and numerous Christian churches, should have created no surprise, he was highly gratified by the zeal and the establishment of his followers. Under the protection of the ample toleration which, they enjoyed, in Poland they were sedulous in their attempts to imprint their tenets upon those among whom they lived, and to send these tenets abroad to foreign nations. The Anti-trinitarians in Poland had early translated the Scriptures, and their successors under Socinus composed many works with the design of defending the principles of their faith. They also sent missionaries to propagate their views and to disseminate the books which supported them, anticipating success similar to that which had accompanied their efforts in Transylvania. But in Hungary and in Austria they were successfully opposed by the united and cordial efforts of Catholics and Protestants. In Holland they were more fortunate: and in England they established only one congregation, which differed in some points from the parent sect, and which soon dwindled away.
These failures, which the ardour, the ability, and the high rank of many who engaged in the diffusion of Socinianism were unable to prevent, were soon followed by their expulsion from the country in which they had so long remained in security and peace. Toward the middle of the seventeenth century some of the students attending the academy at Racow, wantonly insulted the feelings and the principles of the Catholics, by a contemptible act of outrage against a crucifix, which, with stones, they threw down from the place in which it had been erected. By men warmly attached to their own religion, and who had at all times regarded the Socinians as undermining its foundation, this youthful excess was represented as confirming all the charges that had been made against the community to which the perpetrators belonged, and they determined to exert themselves to procure their punishment or extirpation. The supporters of the established religion accordingly applied to the diet at Warsaw; and, notwithstanding the powerful influence used in favour of the Socinians, a cruel edict was passed, abolishing their academy at Racow, banishing the learned men who had taught in it breaking the printing presses, and shutting up the churches. This edict was carried into effect with much severity; but it did not exhaust the enmity now cherished against the sect; for within a few years after, by a solemn act of the Polish diet, they were banished from the territories of the republic. and, with sad departure from the tolerant and beneficent spirit of the Gospel, death was denounced against all who held their opinions, or who even sheltered and protected those who entertained them. A short time was allowed to the unfortunate victims to arrange their affairs before they bade an eternal adieu to scenes which all the ties of human life must have endeared to them; but this period was abridged. Some, however, had escaped the operation of the law, and had remained in Poland; but three years after the edict was renewed, and the Socinians who still lingered in their beloved country were driven from it with a rigour and an inhumanity reflecting infamy upon those who were guilty of them, and leading to the most melancholy reflections upon that dismal perversion of all that is amiable in our nature, which has so often been effected by a mistaken zeal for a religion breathing the tenderest concern for the happiness of mankind. The principles of Socinus were, notwithstanding, secretly fostered, and various causes tended to perpetuate them even where in profession they were abjured. The propensity, so natural to man, of dissipating every shade of mystery, and casting the light of his own understanding around the subjects of his contemplation, did not cease to operate; and the application of this principle, so gratifying to the pride of human reason, carried many farther than even Socinus had probably anticipated.
The Socinians hold, that Jesus Christ was a mere man, who had no existence before he was born of the Virgin Mary; that the Holy Ghost is no distinct person; but that the Father only is truly and properly God. They own that the name of God is given in Scripture to Jesus Christ, but contend that it is only a deputed title; which, however, invests him with a great authority over all creatures. They deny the doctrine of satisfaction and imputed righteousness, and say, that Christ only preached the truth to mankind, set before them in himself an example of heroic virtue, and sealed his doctrines with his blood. Original sin they esteem a mere scholastic chimera. Some of them, likewise, maintain the sleep of the soul, which, they say, becomes insensible at death, and is raised again with the body at the resurrection, when the good shall be established in the possession of eternal felicity, while the wicked shall be consigned to a fire that will torment them, not eternally, but for a certain duration, proportioned to their demerits.
Charles Buck Theological Dictionary 
A sect so called from Faustus Socinus, who died in Poland in 1604. There were two who bore the name Socinus, uncle and nephew, and both disseminated the same doctrine; but it is the nephew who is generally considered as the founder of this sect. They maintain "that Jesus Christ was a mere man, who had no existence before he was conceived by the Virgin Mary; that the Holy Ghost is no distinct person; but that the Father is truly and properly God. They own that the name of God is given in the holy Scriptures to Jesus Christ, but contend that it is only a deputed title, which, however, invests him with a great authority over all created beings. They deny the doctrines of satisfaction and imputed righteousness, and say, that Christ only preached the truth to mankind, set before them in himself an example of heroic virtue, and sealed his doctrines with his blood. Original sin and absolute predestination they esteem scholastic chimeras. Some of them likewise maintain the sleep of the soul, which, they say, becomes insensible at death, and is raised again with the body at the resurrection, when the good shall be established in the possession of eternal felicity, while the wicked shall be consigned to a fire that will not torment them eternally, but for a certain duration proportioned to their demerits."
There is some difference, however, between ancient and modern Socinians. The latter, indignant at the name Socinian, have appropriated to themselves that of Unitarians, and reject the notions of a miraculous conception and the worship of Christ; both which were held by Socinus. Dr. Priestly has laboured hard in attempting to defend this doctrine of the Unitarians, but Dr. Horsley, bishop of Rochester, has ably refuted the doctor in his Theological Tracts, which are worthy the perusal of every Christian, and especially every candidate for the ministry. Dr. Price agreed with the Socinians in the main, yet his system was somewhat different. He believed in the pre-existence of Christ, and likewise that he was more than a human being; and took upon him human nature for a higher purpose than merely revealing to mankind the will of God, and instructing them in their duty and in the doctrines of religion. The Socinians flourished greatly in Poland about the year 1551: and J. Siemienius, palatine of Podolia, built purposely for their use the city of Racow.
A famous catechism was published, called the Racovian catechism: and their most able writers are known by the title of the Polones Fratres, or Polonian Brethren. Their writings were re-published together, in the year 1656, in one great collection, consisting of six volumes in folio, under the title of Bibliotheca Fratrum. An account of these authors may be seen in Dr. Toulmin's Life of Socinus. Some of the writers on the Socinian doctrine, besides the above-mentioned, have been, Haynes in his Scripture Account of the Attributes and Worship of God, and of the Character and Offices of Jesus Christ; Dr. Lardner on the Logos; Priestly's Hist. of early Opinions and Disquisitions; Lindsay in his Historical View of Unitarianism; Carpenter's Unitarianism; and Belsham's Answer to Wilberforce. Against the Socinian doctrine may be consulted, Dr. Horne's Sermon on the Duty of contending for the Faith; Dr. Owen against Biddle; Dr. Hornbeck's Confutation of Socinianism; Calovius's Ditto; Macgowan's Socinianism brought to the Test; and books under articles Arians and Jesus Christ
The Nuttall Encyclopedia 
A sect of the Unitarian body who, in the 16th century, take their name from Faustus Socinus ( q. v .), who, besides denying the doctrine of the Trinity, deny the divinity of Christ and the divine inspiration of Scripture; they arose into importance originally in Poland, and in the 17th century spread by degrees in Prussia, the Netherlands, and England.