Just open for a drink (4)
I believe the answer is:
ajar
'just open' is the definition.
(I've seen this before)
'a drink' is the wordplay.
'drink' becomes 'jar' (colloquial).
'a'+'jar'='AJAR'
'for' acts as a link.
(Other definitions for ajar that I've seen before include "Partially open" , "Half open" , "(Door) to, not shut" , "Half-closed" , "near closing?" .)