cavalier (adj.)

"disdainful," 1650s, from cavalier (n.). Earlier it meant "gallant" (1640s). Related: Cavalierly.

cavalier (n.)

1580s, 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 some Anatolian language. The same source is thought to have yielded Old Church Slavonic kobyla.

Sense advanced in 17c. to "knight," then "courtly gentleman" (but also, pejoratively, "swaggerer"), which led to the adjectival senses, especially "disdainful" (1650s). Meaning "Royalist adherent of Charles I" is from 1641. Meaning "one who devotes himself solely to attendance on a lady" is from 1817, roughly translating Italian cavaliere-servente.