castle (n.)youdaoicibaDictYouDict[castle 词源字典]
late Old English castel "village" (this sense from a biblical usage in Vulgar Latin); later "large fortified building, stronghold," 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" (and perhaps related to castrare via notion of "cut off;" see caste). In early bibles, castle was used to translate Greek kome "village."

This word also had come to 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 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.[castle etymology, castle origin, 英语词源]
lackluster (adj.)youdaoicibaDictYouDict
also lack-luster, c. 1600, first attested in "As You Like It," from lack + luster. Combinations with lack- were frequent in 16c., such as lackland (1590s), of a landless man; lack-Latin (1530s), of an ignorant priest.