Noun
A supplementary glass containing some form of hard spirit, traditionally a whisky, which sits separately alongside one’s pint of ale or stout.
A punter of a drinking establishment who has a pint and a separate spirit
on the go,
simultaneously, is said to be drinking "castle kingside". The act of ordering this
particular drinking setup — assuming the drinker is already on pints but wants an accompanying spirit — is known as “castling”, or “to castle”, from the verb castle.
The term is derived from the chess move of the same name, whereby the king is moved two squares towards a rook (castle) on the player's first rank, then the rook is moved to the square over which the king crossed. The outcome leaves the king and rook side-by-side.
