Castle
late Old English: from Anglo-Norman French and Old Northern French castel, from Latin castellum, diminutive of castrum ‘fort’.
wiktionary
From Middle English castle, castel, from late Old English castel, castell(“a town, village, castle”), borrowed from Late Latin castellum(“small camp, fort”), diminutive of Latin castrum(“camp, fort, citadel, stronghold”), possibly from Proto-Indo-European *kat-(“hut, shed”). Doublet of castell, castellum, and château. Parallel borrowings (from Late Latin or Old French) are Scots castel, castell(“castle”), West Frisian kastiel(“castle”), Dutch kasteel(“castle”), German Kastell(“castle”), Danish kastel(“citadel”), Swedish kastell(“citadel”), Icelandic kastali(“castle”), Welsh castell. The Middle English word was reinforced by Anglo-Norman/Old Northern French castel, itself from Late Latin castellum(“small camp, fort”) (compare modern French château from Old French chastel). If Latin castrum(“camp, fort, citadel, stronghold”) is from Proto-Indo-European *kat-(“hut, shed”), Latin casa(“cottage, hut”) is related. Possibly related also to Gothic 𐌷𐌴𐌸𐌾𐍉( hēþjō, “chamber”), Old English heaþor(“restraint, confinement, enclosure, prison”). See also casino, cassock.
etymonline
castle (n.)
late Old English castel "village" (this sense from a biblical usage in Vulgar Latin); later "large building or series of connected buildings fortified for defense, fortress, stronghold" (late Old English), in this sense from Old North French castel (Old French chastel, 12c.; Modern French château), from Latin castellum "a castle, fort, citadel, stronghold; fortified village," diminutive of castrum "fort," from Proto-Italic *kastro- "part, share;" cognate with Old Irish cather, Welsh caer "town" (probably related to castrare via notion of "cut off," from PIE root *kes- "to cut"). In early bibles, castle was used to translate Greek kome "village."
Latin castrum in its plural castra was used for "military encampment, military post" and thus it came into Old English as ceaster and formed the -caster and -chester in place names. Spanish alcazar "castle" is from Arabic al-qasr, from Latin castrum. Castles in Spain "visionary project, vague imagination of possible wealth" translates 14c. French chastel en Espaigne (the imaginary castles sometimes stood in Brie, Asia, or Albania) and probably reflects the hopes of landless knights to establish themselves abroad. The statement that an (English) man's home is his castle is from 16c.
THAT the house of every man is to him as his castle and fortress, as well for his defence against injuries and violence, as for his repose .... [Edward Coke, "Semaynes Case," 1604]
castle (v.)
chess move involving the king and the rook, recorded under this name from 1650s, from castle (n.), as an old alternative name for the rook. Earlier, the verb meant "fortify (a place) with castles" (c. 1500); "provide (a ship) with fortified towers" (c. 1400); "decorate (a dish) with paper towers, etc." (late 14c.). Related: Castled; castling.
