A bit of syrup in a cola daiquiri (a rum cocktail) (4,6)
I believe the answer is:
pina colada
'a rum cocktail' is the definition.
(I've seen this before)
'a bit of syrup in a cola daiquiri' is the wordplay.
'a bit of' indicates the answer is hidden within the clue (I've seen 'a bit' mean this (the answer is formed by a bit of the clue)).
'PINA COLADA' is hidden within 'syrup in a cola daiquiri'.
(Other definitions for pina colada that I've seen before include "rum-based potation" , "Drink made of pineapple juice, coconut cream and rum" , "alcoholic one" , "Perhaps contents of cocktail glass" , "Cocktail of rum, pineapple juice and coconut" .)