Well up after a fairy's drink (8)
I believe the answer is:
aperitif
'drink' is the definition.
(aperitif is a kind of drink)
'well up after a fairy's' is the wordplay.
'well' becomes 'fit' ('fit' is associated in meaning with 'well'**).
'up' is a reversal indicator (in down clue: letters go upwards).
'after' is a charade indicator (letters next to each other).
'fairy' becomes 'peri' (Persian mythological being).
'fit' reversed gives 'tif'.
'a'+'peri'='aperi'
'tif' put after 'aperi' is 'APERITIF'.
(Other definitions for aperitif that I've seen before include "Preprandial tipple" , "Appetite stimulant drink" , "Pre-dinner drink" , "Alcoholic beverage as an appetiser" , "Alcoholic drink before a meal, like sherry" .)