This adjective, meaning joyful or light-hearted, is of uncertain origin. The English word comes from the French gai, but where this French word comes from is uncertain. There are cognates in other Romance languages, notably Provencal, Old Spanish, Portugeuse, and Italian, but no likely Latin candidate for a root exists. The word is probably Germanic in origin, with the Old High German gāhi, fast or fleeting, suggested as a likely progenitor.1
The word is first recorded in English c.1325, with the meaning of beautiful, in a poem titled Blow, Northerne Wind, which appears in the manuscript British Library MS Harley 2253 (As an aside, Harley 2253 is a very important manuscript. It is a treasure-trove of early English lyric poetry, containing early and unique copies of many poems.):
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Heo is dereworþe in day,
graciouse, stout, ant gay,
gentil, iolyf so þe iay.
(She is precious in day
gracious, stout, and gay,
gentle, jolly as the jay.)2
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