gibbous

adjective

gib·​bous ˈji-bəs  ˈgi- 

1

a

: marked by convexity or swelling

b

of the moon or a planet : seen with more than half but not all of the apparent disk illuminated

2

: having a hump : humpbacked

Did you know?

The adjective gibbous has its origins in the Latin noun gibbus, meaning "hump." It was adopted into Middle English to describe rounded, convex things. While it has been used to describe the rounded body parts of humans and animals (such as the back of a camel) and to describe the shape of certain flowers (such as snapdragons), the term is most often used to describe the moon: a gibbous moon is one that is between half full and full.

Examples of gibbous in a Sentence

Recent Examples on the Web

Unfortunately, the 2025 Perseids happened to coincide with the appearance of a waxing gibbous moon, which bleached the sky with moonlight, blotting out all but the brightest members of the ancient meteor shower. —Anthony Wood, Space.com, 13 Aug. 2025

The moon will be in a waning gibbous phase and at around 85% illumination, which means the light from the moon will make meteor-spotting more difficult. —Gina Park, CNN Money, 12 Aug. 2025

Waning gibbous – The moon heads back towards the sun. —Saleen Martin, USA Today, 11 Aug. 2025

The Perseids are the best annual meteor shower, but this year’s show will be dimmed by a bright gibbous moon One of the best annual meteor showers, the Perseid meteor shower, is peaking now. —Clara Moskowitz, Scientific American, 11 Aug. 2025

Word History

Etymology

Middle English, from Late Latin gibbosus humpbacked, from Latin gibbus hump

First Known Use

14th century, in the meaning defined at sense 1a

Kids Definition

gibbous

adjective

gib·​bous ˈjib-əs  ˈgib- 

: seen with more than half but not all of the disk lighted

gibbous moon

Medical Definition

gibbous

adjective

gib·​bous ˈjib-əs  ˈgib- 

1

: marked by swelling or convexity especially on one side : protuberant

2

: having a hump