A drink only just opened? (4)
I believe the answer is:
ajar
'only just opened?' is the definition.
'a drink' is the wordplay.
'drink' becomes 'jar' (colloquial**).
'a'+'jar'='AJAR'
(Other definitions for ajar that I've seen before include "not entirely open" , "Partially open" , "near closing?" , "A little bit open, like door" , "Not quite closed" .)