Drink? A fairy gets it knocked back, loudly (8)
I believe the answer is:
aperitif
'drink?' is the definition.
(aperitif is a kind of drink)
'a fairy gets it knocked back loudly' is the wordplay.
'fairy' becomes 'peri' (Persian mythological being).
'gets' means one lot of letters go next to another.
'knocked back' says the letters should be written in reverse.
'loudly' becomes 'f' (A musical term).
'it' written backwards gives 'ti'.
'a'+'peri'+'ti'+'f'='APERITIF'
(Other definitions for aperitif that I've seen before include "Alcoholic beverage as an appetiser" , "alcohol before meal" , "An alcoholic drink before dinner, an appetiser" , "Preprandial tipple" , "Alcoholic drink to whet the appetite" .)