Card game requiring composure (8)
I believe the answer is:
patience
This clue is a double definition.
'card game' is the first definition.
(patience is a kind of card game)
'composure' is the second definition.
(I've seen this before)
'requiring' is the link.
(Other definitions for patience that I've seen before include "Gilbertian dairymaid" , "Game, tolerance of delay" , "restraint" , "G & S' alternative for "Bunthorne''s Bride"" , "Quality of endurance in operetta" .)