Shorten a game of cards (7)
I believe the answer is:
abridge
'shorten' is the definition.
(I know that shorten can be written as abridge)
'a game of cards' is the wordplay.
'game of cards' becomes 'bridge' (bridge is a card game).
'a'+'bridge'='ABRIDGE'
(Other definitions for abridge that I've seen before include "Tighten up" , "Crop" , "Shorten, a book say, without losing the sense" , "Cut short" , "Remove sections" .)