The Collaborative International Dictionary of English v.0.48:

Planet \Plan"et\, n. [OE. planete, F. plan[`e]te, L. planeta,
   fr. Gr. ?, and ? a planet; prop. wandering, fr. ? to wander,
   fr. ? a wandering.]
   1. (Astron.) A celestial body which revolves about the sun in
      an orbit of a moderate degree of eccentricity. It is
      distinguished from a comet by the absence of a coma, and
      by having a less eccentric orbit. See Solar system.
      [1913 Webster]

   Note: The term planet was first used to distinguish those
         stars which have an apparent motion through the
         constellations from the fixed stars, which retain their
         relative places unchanged. The inferior planets are
         Mercury and Venus, which are nearer to the sun than is
         the earth; the superior planets are Mars, the
         asteroids, Jupiter, Saturn, Uranus, and Neptune, which
         are farther from the sun than is the earth. Primary
         planets are those which revolve about the sun;
         secondary planets, or moons, are those which revolve
         around the primary planets as satellites, and at the
         same time revolve with them about the sun.
         [1913 Webster]

   2. A star, as influencing the fate of a men.
      [1913 Webster]

            There's some ill planet reigns.       --Shak.
      [1913 Webster]

   Planet gear. (Mach.) See Epicyclic train, under
      Epicyclic.

   Planet wheel, a gear wheel which revolves around the wheel
      with which it meshes, in an epicyclic train.
      [1913 Webster]

WordNet (r) 3.0 (2006):

planet
    n 1: (astronomy) any of the nine large celestial bodies in the
         solar system that revolve around the sun and shine by
         reflected light; Mercury, Venus, Earth, Mars, Jupiter,
         Saturn, Uranus, Neptune, and Pluto in order of their
         proximity to the sun; viewed from the constellation
         Hercules, all the planets rotate around the sun in a
         counterclockwise direction [syn: planet, major planet]
    2: a person who follows or serves another [syn: satellite,
       planet]
    3: any celestial body (other than comets or satellites) that
       revolves around a star

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "planet":
   Earth, Jupiter, Mars, Mercury, Neptune, Pluto, Saturn, Uranus,
   Venus, asteroid, globe, inferior planet, major planet,
   minor planet, planetoid, secondary planet, solar system,
   superior planet, terrestrial planet, wanderer, world



The Free On-line Dictionary of Computing (30 December 2018):

Planet

   ["An Experiment in Language Design for Distributed Systems",
   D. Crookes et al, Soft Prac & Exp 14(10):957-971 (Oct 1984)].