Formal

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late Middle English: from Latin formalis, from forma ‘shape, mould’ (see form).

wiktionary

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From Middle English formel, borrowed from Old French formel, from Latin formalis, from forma(“form”); see form.

see formo-

etymonline

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formal (adj.)

late 14c., "pertaining to form or arrangement;" also, in philosophy and theology, "pertaining to the form or essence of a thing," from Old French formal, formel "formal, constituent" (13c.) and directly from Latin formalis, from forma "a form, figure, shape" (see form (n.)). From early 15c. as "in due or proper form, according to recognized form," As a noun, c. 1600 (plural) "things that are formal;" as a short way to say formal dance, recorded by 1906 among U.S. college students.