Cocktail served as 'cider' (7)
I believe the answer is:
sidecar
'cocktail' is the definition.
(sidecar is a kind of cocktail)
'served as cider' is the wordplay.
'served' indicates anagramming the letters.
'as'+'cider'='ascider'
'ascider' is an anagram of 'SIDECAR'.
(Other definitions for sidecar that I've seen before include "In which Gromit goes" , "In which a passenger may be taken" , "Attachment on motorcycle to carry passenger" , "Tipple" , "One-wheeled compartment attached to a motorcycle" .)