They start in the corners (5)
I believe the answer is:
rooks
'they start in the corners' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rooks that I've seen before include "Overcharges" , "Large, crow-like birds" , "Castles, also, in chess" , "Cheats" , "men on the board" .)