French bridge player to refuse to accept deal, ultimately, without warning (8)
I believe the answer is:
suddenly
'without warning' is the definition.
(thesaurus)
'french bridge player to refuse to accept deal ultimately' is the wordplay.
'french bridge player' becomes 'sud' ('south' in French - bridge players are directions).
'to refuse' becomes 'deny' ('deny' can be a synonym of 'refuse'**).
'to accept' means one lot of letters goes inside another.
'ultimately' suggests the final letters.
The final letter of 'deal' is 'l'.
'deny' enclosing 'l' is 'denly'.
'sud'+'denly'='SUDDENLY'
(Other definitions for suddenly that I've seen before include "Happening without warning" , "Without any warning, unexpectedly" , "In an unexpected manner" , "Unexpectedly, abruptly" , "Fast and unexpectedly" .)