Willing gambler among mediocre employees initially (4)
I believe the answer is:
game
'willing' is the definition.
(thesaurus)
'gambler among mediocre employees initially' is the wordplay.
'initially' suggests taking the first letters.
The initial letters of 'gambler among mediocre employees' is 'GAME'.
(Other definitions for game that I've seen before include "Willing; plucky" , "Lark" , "Animals hunted for food" , "venison, say" , "Competitive activity with rules" .)