Joke with son on board plane (4)
I believe the answer is:
jest
'joke' is the definition.
('jest' can be a synonym of 'joke')
'son on board plane' is the wordplay.
'son' becomes 's'.
'on board' indicates putting letters inside.
'plane' becomes 'jet' (jet plane is a kind of plane).
's' put into 'jet' is 'JEST'.
'with' is the link.
(Other definitions for jest that I've seen before include "Joke, gag" , "Ridicule" , "Piece of humour" , "fun" , "Quip" .)