Eat in drinking establishment (6)
I believe the answer is:
ingest
'eat' is the definition.
(I've seen this before)
'in drinking establishment' is the wordplay.
'in' indicates the answer is hidden within the clue.
'INGEST' is hidden within 'drinking establishment'.
(Other definitions for ingest that I've seen before include "Consume food" , "Absorb mentally" , "Absorb - signet (anag)" , "take in, eat" , "Swallow -signet (anag)" .)