Chessman also called a castle (4)
I believe the answer is:
rook
'chessman also called a castle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rook that I've seen before include "Gregarious black bird" , "Defraud -- crow" , "Gregarious crow" , "Chesspiece otherwise known as a castle" , "A bird; overcharge" .)