Clever bishop, unsettled? (6)
I believe the answer is:
brainy
'clever' is the definition.
(thesaurus)
'bishop unsettled?' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'unsettled?' becomes 'rainy' (rainy weather might be described as unsettled).
'b'+'rainy'='BRAINY'
(Other definitions for brainy that I've seen before include "Intellectual" , "Bright" , "Showing intelligence" , "Clever, got lots of grey matter" , "Highly intelligent" .)