Source : Webster's Revised Unabridged Dictionary (1913)

Arc \Arc\, n. [F. arc, L. arcus bow, arc. See {Arch}, n.]
   1. (Geom.) A portion of a curved line; as, the arc of a
      circle or of an ellipse.

   2. A curvature in the shape of a circular arc or an arch; as,
      the colored arc (the rainbow); the arc of Hadley's
      quadrant.

   3. An arch. [Obs.]

            Statues and trophies, and triumphal arcs. --Milton.

   4. The apparent arc described, above or below the horizon, by
      the sun or other celestial body. The diurnal arc is
      described during the daytime, the nocturnal arc during the
      night.

   {Electric arc}, {Voltaic arc}. See under {Voltaic}.

Source : WordNet®

electric arc
     n : electrical conduction through a gas in an applied electric
         field [syn: {discharge}, {spark}, {arc}, {electric
         discharge}]