Inclined to laugh easily; prone to laughter or a tendency to find things funny.
From Greek 'gelos' (laughter) + suffix '-ose' (full of, characterized by). Created in the 17th-18th century as a medical or humoral term.
In medieval and Renaissance medicine, doctors actually classified people by their tendencies to laugh and their 'gelosity'—it was part of the four humors theory! This word survived longer in English than the actual medical theory it came from.
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