Piece next to a knight (4)
I believe the answer is:
rook
'piece next to a knight' 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" , "Species of crow" , "man in marginalised position, initially" , "Use deceit to get money" , "Chess piece or crow" .)