Confirm drink left on board (7)
I believe the answer is:
support
'confirm' is the definition.
('support' can be a synonym of 'confirm')
'drink left on board' is the wordplay.
'drink' becomes 'sup' (I've seen this before**).
'left on board' becomes 'port' (port is left on board a ship).
'sup'+'port'='SUPPORT'
(Other definitions for support that I've seen before include "Buttress" , "Help; bear" , "Uphold" , "Maintain, back" , "comfort" .)