Title of Osiris
I believe the answer is:
'title' is the definition.
(I've seen this before)
'of osiris?' is the wordplay.
'of' says the answer is hidden in the clue.
'SIR' can be found hidden inside 'osiris'.
(Other definitions for sir that I've seen before include "address to teacher" , "Formal term of address" , "Gentleman's form of address" , "... ___ John Major" , "Feted fellow" .)