Cheerful bishop — just (6)
I believe the answer is:
bright
'cheerful' is the definition.
(thesaurus)
'bishop just' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'just' becomes 'right' (associated in meaning).
'b'+'right'='BRIGHT'
(Other definitions for bright that I've seen before include "Vivid - promising - smart" , "full of promise" , "Clever - shining - sunny" , "Radiant -- clever" , "Cheerful or quick-witted" .)