Grand drink knocked back (5)
I believe the answer is:
regal
'grand' is the definition.
(I've seen this before)
'drink knocked back' is the wordplay.
'drink' becomes 'lager' (lager is a kind of drink).
'knocked back' is a reversal indicator.
'lager' written backwards gives 'REGAL'.
(Other definitions for regal that I've seen before include "befitting a king" , "King-like" , "Royal - lager (anag)" , "Royal - 5 down (anag)" , "Grand and imposing" .)