Definition of: longitude

(lon′ji·td, -tyd) noun
1. Geog. Distance east or west on the earth's surface, measured by the angle which the meridian through a place makes with some standard meridian, as that of Greenwich or Paris. Longitude may be expressed either in time (longitude in time) or in degrees (longitude in arc).
2. Astron. The angular distance from the vernal equinox to the intersection with the ecliptic of the perpendicular from a heavenly body: usually termed celestial longitude, and distinguished as geocentric when the earth's center is assumed as the central point, and heliocentric when the sun's center is taken as the central point.
3. Math. The angle the radius vector makes with the initial meridian axis in the spherical coordinate system. [<F <L longitudo <longus long]