ancient name of England, attested in Old English, from Latin, sometimes said to be from the non-Indo-European base *alb "mountain," which also is suggested as the source of Latin Alpes "Alps," Albania, and Alba, an Irish name for "Scotland." But more likely from Latin albus "white" (see alb), which would be an apt description of the chalk cliffs of the island's southern coast.
Breoton is garsecges ealond, ðæt wæs iu geara Albion haten. [translation of Bede's "Historia Ecclesiastica Gentis Anglorum," c. 900 C.E.]
Perfidious Albion, a reference to the supposedly treacherous policies of Britain when dealing with foreign powers, translates French rhetorical phrase la perfide Albion, said to have been in use since 16c. but popularized by Napoleon in the recruiting drive of 1813.
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]