Osiris' wife (4)
I believe the answer is:
isis
'osiris' wife' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for isis that I've seen before include "Egyptian deity" , "Sister of Osiris" , "Goddess of the rainbow" , "Egyptian goddess - Thames at Oxford" , "Si Si - she's an Egyption goddess" .)