Keep short jack, say, in vehicle (5,3)
I believe the answer is:
stock car
'vehicle' is the definition.
(stock car is a kind of vehicle)
'keep short jack say' is the wordplay.
'keep' becomes 'stock' (I've seen this before).
'short' means to remove the last letter.
'jack say' becomes 'card' (jack is a kind of card).
'card' with its last letter removed is 'car'.
'stock'+'car'='STOCK-CAR'
'in' is the link.
(Other definitions for stock car that I've seen before include "Modified motor for racing and ramming" , "customised vehicle" , "Production-line vehicle modified for racing" , "Type of racing" , "production saloon" .)