from
The Collaborative International Dictionary of English v.0.48
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.
[1913 Webster]
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}.
[1913 Webster]
{Equator of the sun} or {Equator 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}.
[1913 Webster]