gibbous
Americanadjective
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Astronomy. (of a heavenly body) convex at both edges, as the moon when more than half full.
adjective
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(of the moon or a planet) more than half but less than fully illuminated
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having a hunchback; hunchbacked
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bulging
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More than half but less than fully illuminated. Used to describe the Moon or a planet.
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Compare crescent
Other Word Forms
- gibbosely adverb
- gibboseness noun
- gibbously adverb
- gibbousness noun
Etymology
Origin of gibbous
1350–1400; Middle English < Latin gibbōsus humped, equivalent to gibb ( a ) hump + -ōsus -ous
Explanation
Gibbous describes a certain phase of the moon, when it's bulging outward but isn't quite full. A waxing gibbous moon is one that's getting progressively rounder, night after night. Occasionally the adjective gibbous is used for describing something else that protrudes or bulges, like a sleepy kitten's gibbous belly. Usually, though, it's used for the moon. When the moon isn't new (invisible from the earth) or full, it's either crescent or gibbous. Whenever the moon appears larger than a semicircle, but not quite a circle, you can describe it as gibbous.
Vocabulary lists containing gibbous
Over The Moon: Planetary Vocabulary
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Space Science (Astronomy) - Introductory
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The Moon – Introductory
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
“The waning gibbous moon will severely compromise this shower at the time of maximum activity,” notes the American Meteor Society.
From Los Angeles Times • Jul. 29, 2025
Viewing will also be hampered by the waning gibbous moon at 93% of its full illumination and present in the sky throughout the night.
From BBC • Nov. 17, 2024
Even now, however, a waning gibbous moon will still somewhat impede viewing conditions.
From Salon • Oct. 18, 2024
The waxing gibbous moon will set around midnight, ushering in excellent viewing conditions later in the night and predawn hours.
From National Geographic • Dec. 6, 2023
A gibbous moon rose above the shoulder of 27,824-foot Makalu, washing the slope beneath my boots in ghostly light, obviating the need for a headlamp.
From "Into Thin Air" by Jon Krakauer
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
