Swallow gin cocktail, then set off (6)
I believe the answer is:
ingest
'swallow' is the definition.
(I've seen this before)
'gin cocktail then set off' is the wordplay.
'cocktail' indicates anagramming the letters.
'then' is a charade indicator (letters next to each other).
'off' indicates an anagram.
'gin' with letters rearranged gives 'ing'.
'set' is an anagram of 'est'.
'ing'+'est'='INGEST'
(Other definitions for ingest that I've seen before include "Swallow -signet (anag)" , "Gets in (anag.)" , "Take (food) into the body" , "Absorb, assimilate" , "Take nourishment into the body" .)