An Etymological Dictionary of Astronomy and Astrophysics
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1) An orbit that has a high → eccentricity, i.e. is highly elliptical.
2) In Ptolemy's geocentric model, a → deferent which is slightly off-center from the Earth.

→ ex-; → center; → -ic.

Of a planetary orbit, the angle measured from the perihelion position, to the center of the circumscribing auxiliary circle, to the projected position of the planet on the circle. → anomaly; → mean anomaly; → true anomaly.

→ eccentric; → anomaly.

The amount by which the orbit deviates from circularity: e = c/a, where c is the distance from the center to a focus and a the semi-major axis. If e = 0, the orbit is a circle. If e < 1, the orbit is an ellipse, if e > 1 it is a hyperbola, and if e = 1 it is a parabola. The eccentricity is one of the six → orbital elements that define a → Keplerian orbit.

→ eccentric; → -ity.