a fortified, usually walled residence, as of a prince or noble in feudal times.

the chief and strongest part of the fortifications of a medieval city.

a strongly fortified, permanently garrisoned stronghold.

a large and stately residence, esp. one, with high walls and towers, that imitates the form of a medieval castle.

any place providing security and privacy

It may be small, but my home is my castle.

Chess . the rook.

to place or enclose in or as in a castle.

Chess . to move (the king) in castling.

to move the king two squares horizontally and bring the appropriate rook to the square the king has passed over.

(of the king) to be moved in this manner.

noun

acropolis , alcazar , chteau , citadel , donjon , estate house , fasthold , fastness , fort , fortification , fortress , hold , keep , manor , mansion , palace , peel , safehold , seat , stronghold , tower , villanotes:castle and chateau derive from latin castellum , a diminutive form of castrum \'fort\'; chateau is the modern french version that has been borrowed into english \'as is\' , bastille , chateau , rook , villa