John starts with a vacant pause, getting joke (4)
I believe the answer is:
jape
'joke' is the definition.
('jape' can be a synonym of 'joke')
'john starts with a vacant pause' is the wordplay.
'starts with' says to take the initial letters (I've seen 'start with' mean this).
'vacant' means to remove the middle letters.
'pause' with its centre removed is 'pe'.
The initial letter of 'john' is 'j'.
'j'+'a'+'pe'='JAPE'
'getting' is the link.
(Other definitions for jape that I've seen before include "Kid" , "Trick - joke - jest" , "Practical joke, jest" , "Jolly wheeze" , "Lark" .)