Join card game (6)
I believe the answer is:
bridge
This clue is a double definition.
'join' is the first definition.
(bridging is a kind of joining)
'card game' is the second definition.
(bridge is a kind of card game)
(Other definitions for bridge that I've seen before include "Pontoon is one" , "Overpass" , "Hard ridge on the nose" , "pontoon, perhaps" , "Span, connecting structure" .)