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cas·tle (kăsəl)
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n.
1.
a. A large fortified building or group of buildings with thick walls, usually dominating the surrounding country.
b. A fortified stronghold converted to residential use.
c. A large ornate building similar to or resembling a fortified stronghold.
2. A place of privacy, security, or refuge.
3. Games See rook2.
v. cas·tled, cas·tling, cas·tles
v.intr.
Games
To move the king in chess from its own square two empty squares to one side and then, in the same move, bring the rook from that side to the square immediately past the new position of the king.
v.tr.
1. To place in or as if in a castle.
2. Games To move (the king in chess) by castling.

[Middle English castel, from Old English and from Norman French, both from Latin castellum, diminutive of castrum; see kes- in the Appendix of Indo-European roots.]
(click for a larger image)
castle
Raglan Castle near Raglan, Wales

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 
Cas·tle (kăsəl), Vernon Blythe 1887-1918.
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British-born dancer who together with his wife, Irene Foote Castle (1893-1969), gained recognition for innovative dancing.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.