Drink it up as a starter (4)
I believe the answer is:
asti
'a starter' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see a link between them that I can't see?
'drink it up' is the wordplay.
'drink' becomes 'it'.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'it'+'sa'='itsa'
'itsa' reversed gives 'ASTI'.
'as' is the link.
Can you help me to learn more?
(Other definitions for asti that I've seen before include "Italian town producing sparkling wine" , "Capital of a north-west Italian province, known for its sparking wine" , "Italian 'sparkler'" , "Bubbly wine" , "Source of fizz" .)