The quality of being humped, swollen, or protruding; a hump or bulge.
From Latin gibbosus (humped) + -ity (quality or state). The word entered English in the 17th century through scientific and medical terminology, describing physical conditions where something curves or swells outward.
When the moon appears in its gibbous phase—more than half but not quite full—it's literally 'humped'! Astronomers borrowed this exact word to describe that bulging moon shape.
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