Card game depressing seaman (9)
I believe the answer is:
blackjack
'card game' is the definition.
(blackjack is a kind of card game)
'depressing seaman' is the wordplay.
'depressing' becomes 'black' (synonyms).
'seaman' becomes 'jack' (both can mean a sailor).
'black'+'jack'='BLACKJACK'
(Other definitions for blackjack that I've seen before include "A card game in which the object is to beat the bank" , "2 8 [CASINO GAME]" , "Casino card game" , "Vingt-et-un - pirates' ensign" , "Gambling card game" .)