Exclude expensive cover for bishop (5)
I believe the answer is:
debar
'exclude' is the definition.
('debar' can be a synonym of 'exclude')
'expensive cover for bishop' is the wordplay.
'expensive' becomes 'dear' (I've seen this before).
'cover for' means one lot of letters goes inside another.
'bishop' becomes 'b' (abbreviation used in chess).
'dear' going around 'b' is 'DEBAR'.
(Other definitions for debar that I've seen before include "Prevent from doing something" , "Rule out" , "Shut out, preclude" , "Prohibit (from doing something)" , "Exclude, prohibit" .)