Drink cleric knocked back with empty talk (8)
I believe the answer is:
vermouth
'drink' is the definition.
(vermouth is a kind of drink)
'cleric knocked back with empty talk' is the wordplay.
'cleric' becomes 'rev' (abbreviation for Reverend).
'knocked back' shows that the letters should be reversed in order.
'with' says to put letters next to each other.
'empty talk' becomes 'mouth' (mouth can mean boastful talk).
'rev' back-to-front is 'ver'.
'ver'+'mouth'='VERMOUTH'
(Other definitions for vermouth that I've seen before include "It, possibly" , "Wine flavoured with aromatic herbs" , "Herb-flavoured wine drunk with gin" , "Flavoured wine often mixed with gin" , "Flavoured wine used in cocktails" .)