Source : Webster's Revised Unabridged Dictionary (1913)

Equator \E*qua"tor\, n. [L. aequator one who equalizes: cf. F.
   ['e]quateur equator. See {Equate}.]
   1. (Geog.) The imaginary great circle on the earth's surface,
      everywhere equally distant from the two poles, and
      dividing the earth's surface into two hemispheres.

   2. (Astron.) The great circle of the celestial sphere,
      coincident with the plane of the earth's equator; -- so
      called because when the sun is in it, the days and nights
      are of equal length; hence called also the {equinoctial},
      and on maps, globes, etc., the {equinoctial line}.

   {Equator} {of the sun or of a planet} (Astron.), the great
      circle whose plane passes through through the center of
      the body, and is perpendicular to its axis of revolution.
      

   {Magnetic equator}. See {Aclinic}.

Equator \E*qua"tor\, n. [L. aequator one who equalizes: cf. F.
   ['e]quateur equator. See {Equate}.]
   1. (Geog.) The imaginary great circle on the earth's surface,
      everywhere equally distant from the two poles, and
      dividing the earth's surface into two hemispheres.

   2. (Astron.) The great circle of the celestial sphere,
      coincident with the plane of the earth's equator; -- so
      called because when the sun is in it, the days and nights
      are of equal length; hence called also the {equinoctial},
      and on maps, globes, etc., the {equinoctial line}.

   {Equator} {of the sun or of a planet} (Astron.), the great
      circle whose plane passes through through the center of
      the body, and is perpendicular to its axis of revolution.
      

   {Magnetic equator}. See {Aclinic}.

Source : WordNet®

equator
     n 1: an imaginary line around the Earth forming the great circle
          that is equidistant from the north and south poles; "the
          equator is the boundary between the northern and
          southern hemispheres"
     2: a circle dividing a sphere or other surface into two usually
        equal and symmetrical parts