Definition of: castle

(kas′əl, käs′-) noun
1. A strong fortress.
2. Any massive or imposing building; hence, any place of defense and security.
3. A castle–shaped chessman; a rook.
4. A close helmet; casque.
5. A wooden tower on the back of an elephant. See synonyms under FORTIFICATION.
—v. ·tled, ·tling v.t.
1. To place in or as in a castle; fortify.
2. In chess, to move the king two squares to the right or left, at the same time bringing the castle (rook) from that side of the board toward which the king is moved to the square over which the king has passed.
—v.i.
3. In chess, to move the castle and king in this manner. [Fusion of OE castel village and AF castel castle, both <L castellum, dim. of castrum camp, fort]