Clever bishop — rather wet? (6)
I believe the answer is:
brainy
'clever' is the definition.
(I've seen this before)
'bishop rather wet?' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'rather wet?' becomes 'rainy' (wet weather).
'b'+'rainy'='BRAINY'
(Other definitions for brainy that I've seen before include "Intellectual" , "Having a high IQ" , "Bright" , "smart?" , "Intelligent, clever." .)