Egyptian underworld god (6)
I believe the answer is:
osiris
'egyptian underworld god' 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 "once highly esteemed by Egyptians" , "Egyptian god - sis or I (anag)" , "Egypt. god of dead" , "underworld boss" , "Egyptian god of the underworld" .)