Webster's Dictionary 
(n.) One of the principal divinities of Egypt, the brother and husband of Isis. He was figured as a mummy wearing the royal cap of Upper Egypt, and was symbolized by the sacred bull, called Apis. Cf. Serapis.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
according to others, AIRIS or HYSIRIS (Many-eyed), a celebrated Egyptian deity, whose worship was universal throughout Egypt. This name appears in the hieroglyphic texts as early as the 4th dynasty, and is expressed by a throne and an eye; at a later period, that of the 19th, a palanquin is substituted for a throne; and under the Romans, the pupil of the eve for the eye itself. Osiris does not indeed appear to have been universally honored till the time of the 11th and 12th dynasties, or about 1800 B.C., when Abydos, which was reputed to be his burial-place, rose into importance. In the monuments of this age he is called "great god, eternal ruler, dwelling in the west, and lord of Abut" or Abydos. Even at the most remote period individuals after death were supposed to become an Osiris; and all the prayers and ceremonies performed or addressed to them were, in this character, referring to their future life and resurrection. At the time of the 18th dynasty this title of Osiris was prefixed to their names, and continued to be so till the time of the Romans and the fall of paganism.
The Greek and Roman writers greatly differ in their opinions concerning this celebrated god, but they all agree that, as king of Egypt, he took particular care to civilize his subjects, to polish their morals, to give them good and salutary laws, and to teach them agriculture. After he had accomplished a reform at home, Osiris resolved to go and spread cultivation in the other parts of the earth. He left his kingdom to the care of his wife His, and of her faithful minister Hermes or Mercury. The command of his troops at home was left to the trust of Hercules, a warlike officer. In this expedition Osiris was accompanied by his brother Apollo, and by Anubis, Macedo, and Pan. His march was through Ethiopia, where his army was increased by the addition of the Satyrs, a hairy race of monsters, who made dancing and playing on musical instruments their chief study. He afterwards passed through Arabia, and visited the greatest part of the kingdoms of Asia and Europe, where he enlightened the minds of men by introducing among them the worship of the gods, and a reverence for the wisdom of a supreme being. At his return home Osiris found the minds of his subjects roused and agitated. His brother Typhon had raised seditions, and endeavored to make himself popular. Osiris, whose sentiments were always of the most pacific nature, endeavored to convince his brother of his ill conduct, but he fell a sacrifice to the attempt.
Typhon murdered him in asecret apartment, and cut his body to pieces, which were divided among the associates of his guilt. This cruelty incensed His; she revenged her husband's death, and, with her son Orus, she defeated Typhon and the partisans of his conspiracy. She recovered the mangled pieces of her husband's body, the genitals excepted, which the murderer had thrown into the sea; and to render him all the honor which his humanity deserved, she made as many statues of wax as there were mangled pieces of his body. Each statue contained a piece of the flesh of the dead monarch; and His, after she had summoned to her presence one by one the priests of all the different deities in her dominions, gave them each a statue, intimating that in doing so she had preferred them to all the other communities of Egypt, and she bound them by a solemn oath that they would keep secret that mark of her favor, and endeavor to show their sense of it by establishing a form of worship and paying divine homage to their prince. They were further directed to choose whatever animals they pleased to represent the person and the divinity of Osiris, and they were enjoined to pay the greatest reverence to that representative of divinity, and to bury it when dead with the greatest solemnity. To render their establishment more popular, each sacerdotal body had a certain portion of land allotted to them to maintain them, and to defray the expenses which necessarily attended their sacrifices and ceremonial rites. That part of the body of Osiris which had not been recovered was treated with more particular attention by His, and she ordered that it should receive honors more solemn, and at the same time more mysterious than the other members. As Osiris had particularly instructed his subjects in cultivating the ground, the priests chose the ox to represent him, and paid the most superstitious veneration to that animal. Osiris, according to the opinion of some mythologists, is the same as the sun, and the adoration which is paid by different nations to an Anubis, a Bacchus, a Dionysus, a Jupiter, a Pan, etc., is the same as that which Osiris received in the Egyptian temples. His also after death received divine honors as well as her husband; and as the ox was the symbol of the sun, or Osiris, so the cow was the emblem of the moon, or Isis. Nothing can give a clearer idea of the power and greatness of Osiris than this inscription, which has been found on some ancient monuments: "Saturn, the youngest of all the gods, was my father; I am Osiris, who conducted a large and numerous army as far as the deserts of India, and traveled over the greatest part of the world, and visited the streams of the Ister, and the remote shores of the ocean, diffusing benevolence to all the inhabitants of the earth." Osiris was generally represented with a cap on his head like a mitre, with two horns; he held a stick in his left hand, and in his right a whip with three thongs. Sometimes he appears with the head of a hawk, as that bird, by its quick and piercing eyes, is a proper emblem of the sun (Plutarch, In Isid. and Os.; Herodotus, 2:144; Diodorus, i; Homer, Od. 12:323; AElian, De Anim. iii; Lucian, De Dea. Syr.; Pliny, viii).
In the Egyptian Ritual, or "Book of the Dead," and other inscriptions, Osiris is said to be the son of Seb or Saturn, and born of Nu or Rhea; to be the father of Horus by Isis, of Anubis, and of the four genii of the dead. Many mystic notions were connected with Osiris; he was sometimes thought to be the son of Ra, the Sun, or of Atum, the setting Sun, and the Bennu or Phoenix; also to be uncreate, or self-engendered, and he is identified in some instances with the Sun or the Creator, and the Pluto or Judge of Hades. Osiris was born on the first of the Epagomenae, or five additional days of the year. When born, Chroinos or Saturn is said to have given him in charge to Pamyles; having become king of Egypt, he is stated to have civilized the Egyptians, and especially to have taught them agriculture, the culture of the vine, and the art of making beer; he afterwards traveled over the earth, and conquered the people everywhere by his persuasion. During his absence, his kingdom was confided to His, who guarded it strictly, and Set or Typhon, the brother of Osiris (who was born in the third of the Epagomenae), was unable to revolt against him. Typhon had, however, persuaded seventy-two other persons, and Aso, the queen of Ethiopia, to join him in a conspiracy; and, having taken the measure of Osiris, he had a chest made of the same dimensions, richly ornamented and carved, and produced it at a banquet, where he promised to give it to whomsoever it should fit; and when all had lain down and tried it, and it suited none, Osiris at last laid himself down in it, and was immediately covered over by the conspirators, who placed the lid upon it, and fastened it with nails and molten lead. The chest was then hurled into the Nile, and floated down the Tanaitic mouth into the sea. This happened on the seventeenth of the month Athyr, in the twenty-eighth year of the reign or age of Osiris. Khem or Pan, and his attendant deities, discovered the loss of the god; His immediately cut off a lock of hair and went into mourning, and proceeded in search of Anubis, the child of her sister Nephthys by Osiris; and, having found him, brought him up. The chest meanwhile floated to Byblos, and, lodging in a tamarisk became enclosed in the tree, which was cut down by the king, and the trunk, containing the chest and the body of the god, was converted into a pillar to support the roof of the palace.
The goddess proceeded to Byblos, and ingratiated herself with the queen's women by plaiting their hair and imparting to it an ambrosial smell, so that the monarch, whose name was Melcarthus, and his wife, Saosis or Nemanoun, invited her to court to take care of their own child. She endeavored to confer immortality upon him by placing him on a fire, and changing herself into a swallow, flew around the pillar and bemoaned her fate. The queen became alarmed at the danger of her child; His revealed herself, and asked for the pillar of tamarisk wood, which was given her. She then cut it open, and took out the chest, making great lamentations, and subsequently sailed for Egypt, with the eldest of the king's sons. The goddess, intending to visit Horns, her son, at Buto, deposited the chest in an unfrequented spot; but Typhon discovered it by the light of the moon, tore it into fourteen pieces, and distributed each to a home or district. His recovered all by passing the marshes in a boat of papyrus; all except the phallus, which had been eaten by the lepidotus, the phagrus, and oxyrhynchus fish. Subsequently a battle took place between Horus and Typhon or Set, which lasted three days, and ended by Typhon having fetters placed upon him. His, however, liberated Typhon, which so enraged Horus that he tore off her diadem, but Teti or Thoth placed on her the head of a cow instead. Typhon finally accused Horus of illegitimacy; but the question was decided between them by Teti or Thoth and the gods. From Osiris, after his death, and His sprung Harpocrates. Osiris seems to have been finally revived, and to have become the judge of the Karneter or Hades, presiding at the final judgment of souls in the hall of the two Truths, with the forty-two daemons who presided over the capital sins. and awarding to the soul its final destiny. Thoth or Hermes recorded the judgment, and justified the deceased against his accusers, as he had formerly done for Osiris.
Considerable diversity of opinion existed among the ancients themselves as to the meaning of the myth of Osiris. He represented, according to Plutarch, the inundation of the Nile; His, the irrigated land; Horus, the vapors; Buto, the marshes; Nephthys. the edge of the desert; Anubis, the barren soil; Typhon was the sea; the conspirators, the drought; the chest, the river's banks. The Tanaitic branch was the one which overflowed unprofitably; the twenty-eight years, the number of cubits which the Nile rose at Elephantine; Harpocrates, the first shootings of the corn. Such are the naturalistic interpretations of Plutarch; but there appears in the myth the dualistic principle of good and evil, represented by Osiris and Set or Typhon, or again paralleled by the contest of Ra or the Sun, and Apophis or Darkness. The difficulty of interpretation was increased from the form of Osiris having become blended or identified with that of other deities, especially PtahSocharis, the pigmy of Memphis, and the bull Hapis or Apis, the avatar of Ptah. Osiris was the head of a tetrad of deities, whose local worship was at Abydos, but who were the last repetition of the gods of the other nomes of Egypt, and who had assumed a heroic or mortal type. In form, Osiris is always represented swathed or mummied, in allusion to his embalmment; a network, suggestive of the net by which his remains were fished out of the Nile, covers this dress; on his head he wears the cap atf; having at each side the feather of truth, of which he was the lord. This is placed on the horns of a goat. His hands hold the crook and whip, to indicate his governing and directing power; and his feet are based on the cubit of truth; a panther's skin on a pole is often placed before him, and festoons of grapes hang over his shrine, connecting him with Dionysus. As the "good being," or Onnophris the meek-hearted, the celestial or king of heaven, he wears the white or upper crown. Another and rarer type of him represents him as the Tat, or emblem of stability, wearing the crown of. the two Truths upon his head. His worship, at a later time, was extended over Asia Minor, Greece, and Rome, and at an early age had penetrated into Phoenicia, traces of it being found on the coins of Malta and other places. He became introduced along with the Isiac worship into Rome, and had votaries under the Roman empire. But the attacks of the philosophers, and the rise of Christianity, overthrew these exotic deities, who were never popular with the more cultivated portion of the Roman world. See Prichard, Mythology, p. 208; Willinson, Man. and Cust. 4:314; Bunsen, Egypt's Place, 1:414.
The Nuttall Encyclopedia 
One of the principal gods of Egypt, the husband of Isis, who was his sister and the father of Horus, who avenged the wrongs he suffered at the hands of the Earth, his mother, in whose womb he was born and in whose womb he was buried; he was the god of all the earth-born, and subject to the like fate.