The Collaborative International Dictionary of English v.0.48:

Gaul \Gaul\, n. [F. Gaule, fr. L. Gallia, fr. Gallus a Gaul.]
   1. The Anglicized form of Gallia, which in the time of the
      Romans included France and Upper Italy (Transalpine and
      Cisalpine Gaul).
      [1913 Webster]

   2. A native or inhabitant of Gaul.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Gaul
    n 1: a person of French descent [syn: frog, Gaul]
    2: a Celt of ancient Gaul
    3: an ancient region of western Europe that included what is now
       northern Italy and France and Belgium and part of Germany and
       the Netherlands [syn: Gaul, Gallia]