Cavalier (/ˌkævəˈlɪər/) was first used by Roundheads as a term of abuse for the wealthier Royalist supporters of King Charles I and his son Charles II of England during the English Civil War, the Interregnum, and the Restoration (1642 – c. 1679). It was later adopted by the Royalists themselves. Although it referred originally to political and social attitudes and behaviour, of which clothing was a very small part, it has subsequently become strongly identified with the fashionable clothing of the court at the time. Prince Rupert, commander of much of Charles I's cavalry, is often considered to be an archetypal Cavalier.
Cavalier derives from the same Latin root as the French word chevalier (as well as the Spanish word caballero), the Vulgar Latin word , meaning "horseman". Shakespeare used the word cavaleros to describe an overbearing swashbuckler or swaggering gallant in Henry IV, Part 2, in which Shallow says "I'll drink to Master Bardolph, and to all the cavaleros about London".
"Cavalier" is chiefly associated with the Royalist supporters of King Charles I in his struggle with Parliament in the English Civil War. It first appears as a term of reproach and contempt, applied to the followers of King Charles I in June 1642:
1642 (June 10) Propositions of Parlt. in Clarendon v. (1702) I. 504 Several sorts of malignant Men, who were about the King; some whereof, under the name of Cavaliers, without having respect to the Laws of the Land, or any fear either of God or Man, were ready to commit all manner of Outrage and Violence. 1642 Petition Lords & Com. 17 June in Rushw. Coll. III. (1721) I. 631 That your Majesty..would please to dismiss your extraordinary Guards, and the Cavaliers and others of that Quality, who seem to have little Interest or Affection to the publick Good, their Language and Behaviour speaking nothing but Division and War.