Long slice of feta cheese (4)
I believe the answer is:
ache
'long' is the definition.
(synonyms)
'slice of feta cheese' is the wordplay.
'slice of' indicates a hidden word.
'ACHE' is hidden within 'feta cheese'.
(Other definitions for ache that I've seen before include "Hanker" , "burn" , "anguish" , "Hurt; yearn" , "Play up" .)