Bishop has single skull (4)
I believe the answer is:
bone
'skull' is the definition.
(thesaurus)
'bishop has single' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'has' is a charade indicator (letters next to each other).
'single' becomes 'one' (I've seen this before).
'b'+'one'='BONE'
(Other definitions for bone that I've seen before include "Part of skeleton" , "Eg, rib" , "Skeleton substance" , "Skeleton material" , "Ossified material" .)