Heard plan for a drink (7)
I believe the answer is:
draught
'a drink' is the definition.
(draught is a kind of drink)
'heard plan' is the wordplay.
'heard' shows a homophone (sound like).
'plan' becomes 'draft' (drafting is a kind of planning).
'draft' sounds like 'DRAUGHT'.
'for' is the link.
(Other definitions for draught that I've seen before include "It may be drunk" , "Swallow" , "it's felt, when short of cash" , "Dose of medicine" , "Current - drink - drawing - checker" .)