Father of Horus (6)
I believe the answer is:
'father of horus' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for osiris that I've seen before include "underworld boss" , "Husband of Isis, father of Horus - sis or I (anag)" , "dead judge?" , "Egypt. god of dead" , "one held to be divine" .)