Formidable

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late Middle English: from French, or from Latin formidabilis, from formidare ‘to fear’.

wiktionary

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Borrowed from Middle French formidable, from Latin formīdābilis(“formidable, terrible”), from formīdō(“fear, dread”).

etymonline

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formidable (adj.)

mid-15c., "causing fear," from Old French formidable (15c.), from Latin formidabilis "causing fear, terrible," from formidare "to fear," from formido "fearfulness, fear, terror, dread." Sense has softened somewhat over time, in the direction of "so great (in strength, size, etc.) as to discourage effort." Related: Formidably.