[ plan-i-ter-ee ]
/ ˈplæn ɪˌtɛr i /


of, relating to, or resembling a planet or the planets.
wandering; erratic.
terrestrial; global.
Machinery. noting or pertaining to an epicyclic gear train in which a sun gear is linked to one or more planet gears also engaging with an encircling ring gear.


Machinery. a planetary gear train.

Nearby words

  1. planet x,
  2. planet zog,
  3. planet-struck,
  4. planetarian,
  5. planetarium,
  6. planetary nebula,
  7. planetary precession,
  8. planetesimal,
  9. planetesimal hypothesis,
  10. planetoid

Origin of planetary

From the Latin word planētārius, dating back to 1585–95. See planet, -ary

Related formsnon·plan·e·tar·y, adjective

Can be confusedplanetary plenary plentiful plenitude Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for planetary

British Dictionary definitions for planetary


/ (ˈplænɪtərɪ, -trɪ) /


noun plural -taries

a train of planetary gears
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for planetary



1590s; see planet + -ary. Probably from Late Latin planetarius "pertaining to a planet or planets," but this is attested only as "an astrologer." Planetary nebula, so called for its shape, attested from 1785.

Online Etymology Dictionary, © 2010 Douglas Harper

Science definitions for planetary


[ plănĭt ]

In the traditional model of solar systems, a celestial body larger than an asteroid or comet, illuminated by light from a star, such as the Sun, around which it revolves.
A celestial body that orbits the Sun, has sufficient mass to assume nearly a round shape, clears out dust and debris from the neighborhood around its orbit, and is not a satellite of another planet. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was considered to be a planet until its reclassification in 2006 as a dwarf planet. A planetlike body with more than about ten times the mass of Jupiter would be considered a brown dwarf rather than a planet. See also extrasolar planet inner planet outer planet.
Related formsplanetary adjective

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.