Charles Buck Theological Dictionary 
A class of people whose distinguishing character it is, not to profess any particular form or system of religion; but only to acknowledge the existence of a God, and to follow the light and law of Nature, rejecting revelation and opposing Christianity. The name of deists seems to have been first assumed, as the denomination of a party, about the middle of the 16th century, by some gentlemen in France and Italy, who were desirous of thus disguising their opposition to Christianity by a more honourable appellation than that of atheists. Viret, an eminent reformer, mentions certain persons in his epistle dedicatory, prefixed to the second volume of his Instruction Chretienne, published in 1653, who called themselves by a new name, that of deists. These, he tells us, professed to believe in God, but shewed no regard to Jesus Christ, and considered the doctrine of the apostles and evangelists as fables and dreams. He adds, that they laughed at all religion, though they outwardly conformed to the religion of those with whom they lived, or whom they wished to please, or feared to offend.
Some, he observed, professed to believe the immortality of the soul; others denied both this doctrine and that of providence. Many of them were considered as persons of acute and subtile genius, and took pains in disseminating their notions. The deists hold, that, considering the multiplicity of religions, the numerous pretences to revelation, and the precarious arguments generally advanced in proof thereof, the best and surest way is to return to the simplicity of nature, and the belief of one God; which is the only truth agreed to by all nations. They complain, that the freedom of thinking and reasoning is oppressed under the yoke of religion, and that the minds of men are tyrannized over, by the necessity imposed on them of believing inconceivable mysteries; and contend that nothing should be required to be assented to or believed but what their reason clearly conceives.
The distinguishing character of modern deists is, that they discard all pretences to revelation as the effects of imposture or enthusiasm. They profess a regard for natural religion, though they are far from being agreed in their notions concerning it. They are classed by some of their own writers into mortal and immortal deists; the latter acknowledging a future state; and the former denying it, or representing it as very uncertain. Dr. Clarke distinguishes four sorts of deists.
1. Those who pretend to believe the existence of an eternal, infinite, independent, intelligent Being, who made the world, without concerning himself in the government of it.
2. Those who believe the being and natural providence of God, but deny the difference of actions as morally good or evil, resolving it into the arbitrary constitution of human laws; and therefore they suppose that God takes no notice of them. With respect to both these classes, he observes that their opinions can consistently terminate in nothing but downright atheism.
3. Those who, having right apprehensions concerning the nature, attributes, and all-governing providence of God, seem also to have some notion of his moral perfections; though they consider them as transcendent, and such in nature and degree, that we can form no true judgment, nor argue with any certainty concerning them: but they deny the immortality of human soul; alleging that men perish at death, and that the present life is the whole of human existence.
4. Those who believe the existence, perfections, and providence of God, the obligations of natural religion, and a state of future retribution, on the evidence of the light of Nature, without a divine revelation; such as these, he says, are the only true deists: but their principles, he apprehends, should lead them to embrace Christianity; and therefore he concludes that there is now no consistent scheme of deism in the world. The first deistical writer of any note that appeared in this country was Herbert, baron of Cherbury.
He lived and wrote in the seventeenth century. His book Dr. Veritate was first published at Paris in 1624. This, together with his book De Causis Errorum, and his treatise De Religione Laici, were afterwards published in London. His celebrated work Dr. Religione Gentilium was published at Amsterdam in 1663 in 4to., and in 1700 in 8vo.; and an English translation of it was published at London in 1705. As he was one of the first that formed design into a system, and asserted the sufficiency, universality, and absolute perfection of natural religion, with a view to discard all extraordinary revelation as useless and needless, we shall subjoin the five fundamental articles of this universal religion. They are these:
1. There is one supreme God.
2. That he is chiefly to be worshipped.
3. That piety and virtue are the principal part of his worship.
4. That we must repent of our sins; and if we do so, God will pardon them.
5. That there are rewards for good men and punishments for bad men, both here and hereafter. A number of advocates have appeared in the same cause; and however they may have differed among themselves, they have been agreed in their attempts of invalidating the evidence and authority of divine revelation. We might mention Hobbes, Blount, Toland, Collins, Woolston, Tindall, Morgan, Chubb, lord Bolingbroke, Hume, Gibbon, Paine, and some add lord Shaftesbury to the number. Among foreigners, Voltaire, Rousseau, Condorcet, and many other celebrated French authors, have rendered themselves conspicuous by their deistical writings.
"But, " as one observes, "the friends of Christianity have no reason to regret the free and unreserved discussion which their religion has undergone. Objections have been stated and urged in their full force, and as fully answered; arguments and raillery have been repelled: and the controversy between Christians and deists has called forth a great number of excellent writers, who have illustrated both the doctrines and evidences of Christianity in a manner that will ever reflect honour on their names, and be of lasting service to the cause of genuine religion, and the best interests of mankind."
See articles Christianity, Infidelity, Inspiration and Scripture in this work. Leland's View of Deistical Writers; Sermons at Boyle's Lecture; Halyburton's Natural Religion insufficient; Leslie's Short Method with the Deists; Bishop Watson's Apology for the Bible; Fuller's Gospel of Christ its own Witness; Bishop Porteus's Charge to the Clergy, for 1794; and his summary of the Evidences of Christianity.
Watson's Biblical & Theological Dictionary 
This term appears to have had an honourable origin, being of the same import as Theists, designating those who believe in the existence of a supreme intelligent cause, in opposition to the Epicureans, and other Atheistical philosophers. The name, in modern times, is said to have been first assumed about the middle of the sixteenth century, by some persons on the continent, in order to avoid the imputation of Atheism. Peter Viret, a divine of that century, mentions it as a new name assumed by those who rejected Christianity. Lord Edw. Herbert, baron of Cherbury, in the seventeenth century, has been regarded as the first Deistical writer in this country, or at least, the first who reduced Deism to a system; affirming the sufficiency of reason and natural religion, and rejecting divine revelation as unnecessary and superfluous. His system, however, embraced these five articles:—
1. The being of God.
2. That he is to be worshipped.
3. That piety and moral virtue are the chief parts of worship.
4. That God will pardon our faults on repentance. And,
5. That there is a future state of rewards and punishment.
Some have divided all Deists into two classes—those who admit a future state, and those who deny it. But Dr. S. Clarke, taking the term in the most extensive sense, arranges them under four classes:—
1. Those who admit a Supreme Being, but deny that he concerns himself with the conduct or affairs of men; maintaining, with Lucretius, that God
"Ne'er smiles at good, nor frowns at wicked, deeds."
2. Those who admit not only the being but the providence of God, with respect to the natural world; but who allow no difference between moral good and evil, nor that God takes any notice of our moral conduct.
3. Such as believe in the natural attributes of God, and his all-governing providence; yet deny the immortality of the soul, or any future state.
4. Such as admit the existence of God, his providence, and the obligations of natural religion; but so far only as these things are discoverable by the light of nature, without any divine revelation. Some of the Deists have attempted to overthrow the Christian dispensation, by opposing to it what they call the absolute perfection of natural religion. Others, as Blount, Collins, and Morgan, have endeavoured to gain the same purpose, by attacking particular parts of the Christian scheme, by explaining away the literal sense and meaning of certain passages, or by placing one portion of the sacred canon in opposition to the other. A third class, wherein we meet with the names of Shaftesbury and Bolingbroke, advancing farther in their progress, expunge from their creed the doctrine of future existence, deny or controvert all the moral perfections of the Deity, and wholly reject the Scriptures.
The Deists of the present day are distinguished by their zealous efforts to diffuse the principles of infidelity among the common people. Hume, Bolingbroke, and Gibbon, addressed themselves solely to the more polished classes of the community; but of late the writings of Paine, Carlile, and others, have diffused infidelity among the lower orders of society, and clothed it in the dress of vulgar ridicule, the more effectually to destroy in the common people all reverence for sacred things. Among the disciples of this school, Deism has led to the most disgusting Atheism. Thus "evil men and seducers wax worse and worse."
The Nuttall Encyclopedia 
A set of free-thinkers of various shades, who in England, in the 17th and 18th centuries, discarded revelation and the supernatural generally, and sought to found religion on a purely rational basis.