Inept

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mid 16th century (in the sense ‘not apt, unsuitable’): from Latin ineptus, from in- ‘not’ + aptus (see apt).

wiktionary

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Borrowed from Middle French inepte, from Latin ineptus, from in- + aptus (whence English apt).

etymonline

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inept (adj.)

c. 1600, "not fit or suitable, inapt," also "absurd, foolish," from French inepte "incapable" (14c.) or directly from Latin ineptus "unsuitable, improper, impertinent; absurd, awkward, silly, tactless," from in- "not, opposite of" (see in- (1)) + aptus "apt" (see apt). Related: Ineptly; ineptness.