ecliptic

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The intersection plane of the earth's orbit with the celestial sphere, along which the sun appears to move as viewed from the earth.
2. n. A great circle inscribed on a terrestrial globe inclined at an approximate angle of 23°27ʹ to the equator and representing the apparent motion of the sun in relation to the earth during a year.

Century Dictionary and Cyclopedia

1. Pertaining to an eclipse.
2. Pertaining to the apparent path of the sun in the heavens: as, ecliptic constellations.
3. n. In astronomy, a great circle of the heavens in the plane of the earth's orbit, or that of the apparent annual motion of the sun among the stars. The fixed ecliptic is the position of the ecliptic at any given date. The mean ecliptic is the position of the fixed ecliptic relative to the equinoctial, as modified by precession. This is now approaching the equinoctial at the rate of 47′ ′ per century. The true or apparent ecliptic is the mean ecliptic as modified by the effects of nutation. The obliquity of the ecliptic is the inclination of the ecliptic to the equinoctial. Its mean value for a. d. 1900 is 23° 27′ 8′ ′ .
4. n. A great circle drawn upon a terrestrial globe, tangent to the tropics. It is sometimes said to “mark the sun's annual path across the surface of the earth”; but since its plane is represented as fixed upon the earth, the rotation of the latter will give it a gyratory motion incompatible with its representing any celestial appearance. It may, however, prove convenient when a terrestrial globe is used instead of a celestial one.

Wiktionary

1. n. : The apparent path of the sun in the sky. More accurately, it is the intersection of the celestial sphere with the plane of the ecliptic, which is the geometric plane containing the mean orbit of the Earth around the Sun. So named because an eclipse can occur only when the Moon lies on this plane.

GNU Webster's 1913

1. n. A great circle of the celestial sphere, making an angle with the equinoctial of about 23° 28'. It is the apparent path of the sun, or the real path of the earth as seen from the sun.
2. n. A great circle drawn on a terrestrial globe, making an angle of 23° 28' with the equator; -- used for illustrating and solving astronomical problems.
3. adj. Pertaining to the ecliptic.
4. adj. Pertaining to an eclipse or to eclipses.

WordNet 3.0

1. n. the great circle representing the apparent annual path of the sun; the plane of the Earth's orbit around the sun; makes an angle of about 23 degrees with the equator