The Collaborative International Dictionary of English v.0.48:

Arab \Ar"ab\ (?; 277), n. [Prob. ultimately fr. Heb. arabah a
   desert, the name employed, in the Old Testament, to denote
   the valley of the Jordan and Dead Sea. Ar. Arab, Heb. arabi,
   arbi, arbim: cf. F. Arabe, L. Arabs, Gr. ?.]
   One of a swarthy race occupying Arabia, and numerous in
   Syria, Northern Africa, etc.
   [1913 Webster]

   Street Arab, a homeless vagabond in the streets of a city,
      particularly and outcast boy or girl. --Tylor.
      [1913 Webster]

            The ragged outcasts and street Arabs who are
            shivering in damp doorways.           --Lond. Sat.
                                                  Rev.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Arab
    n 1: a member of a Semitic people originally from the Arabian
         peninsula and surrounding territories who speaks Arabic and
         who inhabits much of the Middle East and northern Africa
         [syn: Arab, Arabian]
    2: a spirited graceful and intelligent riding horse native to
       Arabia [syn: Arabian, Arab]