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[gib-uh s] /ˈgɪb əs/
Astronomy. (of a heavenly body) convex at both edges, as the moon when more than half full.
Also, gibbose
[gib-ohs] /ˈgɪb oʊs/ (Show IPA)
Origin of gibbous
1350-1400; Middle English < Latin gibbōsus humped, equivalent to gibb(a) hump + -ōsus -ous
Related forms
gibbously, gibbosely, adverb
gibbousness, gibboseness, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for gibbous
  • Sometimes it's a waning gibbous phase, low in the west at sunrise.
  • Most noticeable are the half-moon and football-shaped gibbous moon, phases separated by two or three days.
  • The crescent and gibbous phases happen in between those times.
British Dictionary definitions for gibbous


(of the moon or a planet) more than half but less than fully illuminated
having a hunchback; hunchbacked
Derived Forms
gibbously, adverb
gibbousness, noun
Word Origin
C17: from Late Latin gibbōsus humpbacked, from Latin gibba hump
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
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Word Origin and History for gibbous

c.1400, "bulging, convex," from Late Latin gibbus "hunchbacked," from Latin gibbus "hump, hunch," of uncertain origin. Of the moon from early 15c.; also used from 15c. of hunchbacks.

Online Etymology Dictionary, © 2010 Douglas Harper
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gibbous in Medicine

gibbous gib·bous (gĭb'əs)

  1. Characterized by convexity; protuberant.

  2. Having a hump; humpbacked.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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gibbous in Science
More than half but less than fully illuminated. Used to describe the Moon or a planet. Compare crescent.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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