Cavalier
mid 16th century: from French, from Italian cavaliere, based on Latin caballus ‘horse’. Compare with caballero and chevalier.
wiktionary
[1589] Borrowed from Middle French cavalier(“horseman”), [1] itself borrowed from Old Italian cavaliere(“mounted soldier, knight”), [2] borrowed from Old Occitan cavalier, from Late Latin caballārius(“horseman”), from Latin caballus(“horse”), probably from Gaulish caballos 'nag', variant of cabillos (compare Welsh ceffyl, Breton kefel, Irish capall), akin to German (Swabish) Kōb 'nag' and Old Church Slavonic кобꙑла(kobyla) 'mare'.
Previous English forms include cavalero and cavaliero.
etymonline
cavalier (n.)
1580s, "a horseman," especially if armed, from Italian cavalliere "mounted soldier, knight; gentleman serving as a lady's escort," from Late Latin caballarius "horseman," from Vulgar Latin *caballus, the common Vulgar Latin word for "horse" (and source of Italian cavallo, French cheval, Spanish caballo, Irish capall, Welsh ceffyl), displacing Latin equus (from PIE root *ekwo-).
In classical Latin caballus was "work horse, pack horse," sometimes, disdainfully, "hack, nag." This and Greek kaballion "workhorse," kaballes "nag" probably are loan-words, perhaps from an Anatolian language. The same source is thought to have yielded Old Church Slavonic kobyla.
The sense was extended in Elizabethan English to "a knight; a courtly gentleman," but also, pejoratively, "a swaggerer." Meaning "Royalist, adherent of Charles I" is from 1641.
cavalier (adj.)
"disdainful," by 1817, from earlier sense "easy, offhand" (1650s); originally "gallant, knightly, brave" (1640s), from cavalier (n.) in its Elizabethan senses. Related: Cavalierly.
