castle

UK: /ˈkɑːs^əl/ US: /ˈkæsəl/ ,(kas′əl, kä′səl)

Inflections of 'castle' (v): (⇒ conjugate)

castles

v 3rd person singular

castling

v pres p

castled

v past

castled

v past p

WordReference Random House Learner's Dictionary of American English © 2026

cas•tle /ˈkæsəl/   n., v., -tled, -tling. 
n. [countable]

1. a fortified, protected building, usually with a wall around it, owned by a prince or noble esp. in former times.
2. a large and stately residence, esp. one that imitates the forms of a medieval castle.
3. any place providing security and privacy:
   the old saying, a man's home is his castle.
4. Chess Chess. the rook;
   one of the two corner pieces in the first row.

v. 

5. Chess Chess. to move (the king) two squares to the side and bring the rook to the square the king has passed over: [~ + object]
   He castled his king as a final defense.
   [no object]
   He tried castling to protect his king.

WordReference Random House Unabridged Dictionary of American English © 2026

cas•tle  (kas′əl, kä′səl), n., v., -tled, -tling. 
n. 

1. a fortified, usually walled residence, as of a prince or noble in feudal times.
2. the chief and strongest part of the fortifications of a medieval city.
3. a strongly fortified, permanently garrisoned stronghold.
4. a large and stately residence, esp. one, with high walls and towers, that imitates the form of a medieval castle.
5. any place providing security and privacy:
   It may be small, but my home is my castle.
6. Chess the rook.

v.t. 
7. to place or enclose in or as in a castle.
8. Chess to move (the king) in castling.

v.i. Chess. 
9. Chess to move the king two squares horizontally and bring the appropriate rook to the square the king has passed over.
10. Chess (of the king) to be moved in this manner.
• Latin castellum castellum
• Middle English, Old English castel bef. 1000
cas′tle•like′, adj. 
Synonyms
• 1. fortress, citadel.
• 4. palace, château.

Cas•tle  (kas′əl, kä′səl), n. 

1. Biographical Irene (Foote), 1893–1969, born in the U.S., and her husband and partner Vernon (Vernon Castle Blythe), 1887–1918, born in England, U.S. ballroom dancers.

Castle, The, 

1. Literature (German, Das Schloss), a novel (1926) by Franz Kafka.

Collins Concise English Dictionary © HarperCollins Publishers::

castle / ˈkɑːs^əl/ noun

1. a fortified building or set of buildings, usually permanently garrisoned, as in medieval Europe
2. any fortified place or structure
3. a large magnificent house, esp when the present or former home of a nobleman or prince
4. the citadel and strongest part of the fortifications of a medieval town
5. another name for rook2

verb

1. to move (the king) two squares laterally on the first rank and place the nearest rook on the square passed over by the king, either towards the king's side (castling short) or the queen's side (castling long)

Etymology: 11th Century: from Latin castellum, diminutive of castrum fort