"Sleuth" co-star
I believe the answer is:
olivier
'sleuth co-star' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for olivier that I've seen before include "Laurence (Lord) ---, actor" , "English actor and director, died 1989" , "Great player" , "- Messiaen, Twentieth century French composer" , "O! Virile (anag) - English actor, d. 1989" .)