Male wearing waistcoat makes cocktail (6)
I believe the answer is:
gimlet
'cocktail' is the definition.
(gimlet is a kind of cocktail)
'male wearing waistcoat' is the wordplay.
'male' becomes 'm' (common abbreviation).
'wearing' means one lot of letters goes inside another.
'waistcoat' becomes 'gilet' (I've seen this before).
'm' inserted inside 'gilet' is 'GIMLET'.
'makes' acts as a link.
(Other definitions for gimlet that I've seen before include "Hand tool for boring holes" , "Hole-boring tool" , "Something for boring; cocktail" , "A carpenter's tool" , "Small hand tool - cocktail of vodka or gin with lime juice" .)