A drink for the setter, perhaps, if possible? (8)
I believe the answer is:
aperitif
'possible?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a drink for the setter perhaps if' is the wordplay.
'a drink for' becomes 'aper' (I can't justify this - if you can you should give a lot more credence to this answer).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'setter' becomes 'I' (the person that set the crossword).
'perhaps' indicates anagramming the letters.
't'+'i'='ti'
'ti' with letters rearranged gives 'it'.
'aper'+'it'+'if'='APERITIF'
Can you help me to learn more?
(Other definitions for aperitif that I've seen before include "Preprandial drink" , "Pre-dinner drink" , "What's drunk before a meal?" , "Alcoholic drink taken before meal" , "appetizer" .)