castles is a form of:

Castle



noun
1.
(a large fortified building or group of buildings, a chess piece also called a rook. -castle builder daydreamer. -castle in the air, castle in Spain daydream) ប្រាសាទ, ផ្ទះថ្មធំ, ប៉ម
ENGLISH MEANING
noun
1.
A fortified residence, especially that of a prince or nobleman; a fortress.
2.
Any strong, imposing, and stately mansion.
3.
A small tower, as on a ship, or an elephant's back.
4.
A piece, made to represent a castle, used in the game of chess; a rook.
verb
1.
(INTRANSITIVE) To move the castle to the square next to king, and then the king around the castle to the square next beyond it, for the purpose of covering the king.