The Collaborative International Dictionary of English v.0.48:

Osiris \O*si"ris\, prop. n. [L., fr. Gr. ?; of Egyptian origin.]
   (Myth.)
   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. -- O*sir"i*an, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Osiris
    n 1: Egyptian god of the underworld and judge of the dead;
         husband and brother of Isis; father of Horus