Incurable

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Middle English: from Old French, or from late Latin incurabilis, from in- ‘not’ + curabilis (see curable).

wiktionary

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From Old French incurable, from Late Latin incurabilis

etymonline

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incurable (adj.)

mid-14c., from Old French incurable "not curable" (13c.), from Late Latin incurabilis "not curable," from in- "not" (see in- (1)) + curabilis "curable" (see curable). As a noun, "incurable person," from 1650s. Related: Incurably.