When a coin tossed during a game of Feck lodged on its edge in the ground and remains on edge, it is called a 'Cocker' i.e. it does not indecate decisively either 'head' or 'harp' (or tails) and the coin must be tossed again.
Unknown, but note 'used to tilt of various things, e.g. a hat'. (Wright)