Vessel beginning to heel in drink (4)
I believe the answer is:
ship
'vessel' is the definition.
(ship is a kind of vessel)
'beginning to heel in drink' is the wordplay.
'beginning to' says to take the initial letters.
'in' is an insertion indicator.
'drink' becomes 'sip' (sipping is a kind of drinking**).
The initial letter of 'heel' is 'h'.
'h' inserted into 'sip' is 'SHIP'.
(Other definitions for ship that I've seen before include "In a word, final indication of rank or position" , "Large boat, dispatch" , "Ocean-going vessel" , "Large sailing vessel" , "craft of 1d [ADVENTURE]" .)