planetary

American  

[plan-i-ter-ee] / ˈplæn ɪˌtɛr i /

adjective

1. of, relating to, or resembling a planet or the planets.

2. wandering; erratic.

3. terrestrial; global.

4. 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.

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noun

1. Machinery. a planetary gear train.

planetary British  

/ ˈplænɪtərɪ, -trɪ /

adjective

1. of or relating to a planet

2. mundane; terrestrial

3. wandering or erratic

4. astrology under the influence of one of the planets

5. (of a gear, esp an epicyclic gear) having an axis that rotates around that of another gear

6. (of an electron) having an orbit around the nucleus of an atom

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noun

1. a train of planetary gears

Other Word Forms

• nonplanetary
  adjective

Etymology

Origin of planetary

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

Explanation

The adjective planetary has to do with any astronomical body that revolves around a star — including the earth. Rather than a circle, planetary motion takes us in an elliptical shape around the sun. In science, planetary usually describes the attributes or motion of planets. It's also used for anything that behaves in a similar way, like planetary electrons, which revolve around their atomic nucleus as if they were tiny planets. You can also talk about things that affect our entire planet using this word: "She worries a lot about the planetary effects of climate change."

Example Sentences

This time, Earth’s most elite fighters face off against the forces of an evil emperor—and one another—in a battle for planetary survival.

From The Wall Street Journal • May 3, 2026

It would take the early 20th century’s sharper telescopes and planetary photography to quell the buzz about smart alien neighbors.

From The Wall Street Journal • Apr. 23, 2026

Astronomers typically interpret such data by comparing observations with computer models of planetary atmospheres.

From Science Daily • Apr. 22, 2026

Benjamin Fernando, a seismologist and planetary scientist at Johns Hopkins University, happened to be in an Ohio city during the event.

From Science Daily • Apr. 18, 2026

Modern planetary scientists sometimes argue that the collision of a comet with a planet might make a significant contribution to the planetary atmosphere.

From "Cosmos" by Carl Sagan

Related Words

• global
• terrestrial