Black bishop in commercial activity (5)
I believe the answer is:
sable
'black' is the definition.
(sable is a kind of black)
'bishop in commercial activity' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'in' is an insertion indicator.
'commercial activity' becomes 'sale' (I've seen this in other clues).
'b' placed within 'sale' is 'SABLE'.
(Other definitions for sable that I've seen before include "fur coat" , "Brush" , "Antelope, fur" , "Adventurous courage" , "(Fur from) small carnivore" .)