The Collaborative International Dictionary of English v.0.48:

Cavalier \Cav`a*lier"\ (k[a^]v`[.a]*l[=e]r"), n. [F. cavalier,
   It. cavaliere, LL. caballarius, fr. L. caballus. See
   Cavalcade, and cf. Chevalier, Caballine.]
   1. A military man serving on horseback; a knight.
      [1913 Webster]

   2. A gay, sprightly, military man; hence, a gallant.
      [1913 Webster]

   3. One of the court party in the time of king Charles I. as
      contrasted with a Roundhead or an adherent of Parliament.
      --Clarendon.
      [1913 Webster]

   4. (Fort.) A work of more than ordinary height, rising from
      the level ground of a bastion, etc., and overlooking
      surrounding parts.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cavalier \Cav`a*lier"\, a.
   offhand; unceremonious; gay; easy; frank. Opposed to
   serious.
   [1913 Webster +PJC]

         The plodding, persevering scupulous accuracy of the
         one, and the easy, cavalier, verbal fluency of the
         other, form a complete contrast. --Hazlitt.
   [1913 Webster]

   2. High-spirited. [Obs.] "The people are naturally not
      valiant, and not much cavalier." --Suckling.
      [1913 Webster]

   3. Supercilious; haughty; disdainful; curt; brusque.
      [1913 Webster]

   4. Of or pertaining to the party of King Charles I. "An old
      Cavalier family." --Beaconsfield.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cavalier
    adj 1: given to haughty disregard of others [syn: cavalier,
           high-handed]
    n 1: a gallant or courtly gentleman [syn: cavalier,
         chevalier]
    2: a royalist supporter of Charles I during the English Civil
       War [syn: Cavalier, Royalist]