Pressure before argument in part of boat (4)
I believe the answer is:
prow
'part of boat' is the definition.
(I know that prow is part of boat)
'pressure before argument' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'before' says to put letters next to each other.
'argument' becomes 'row' (to row is to argue).
'p'+'row'='PROW'
'in' is the link.
(Other definitions for prow that I've seen before include "Ship's front part" , "Front of boat" , "Projecting front part of ship" , "Boat's bow" , "position of figurehead" .)