Garnish for a martini (5)
I believe the answer is:
olive
'garnish for a martini' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for olive that I've seen before include "Oil-yielding fruit" , "A Med. fruit" , "Cocktail fruit" , "Girl's name; tree" , "Type of green" .)