Believe in drink? (7)
I believe the answer is:
swallow
I believe this is a double definition.
'believe' is the first definition.
(to swallow something is to accept or believe it)
'drink?' is the second definition.
(swallow a drink)
'in' acts as a link.
(Other definitions for swallow that I've seen before include "flier" , "Accept" , "put up with" , "Creature which can go up" , "Long-winged, fork-trailed bird" .)