inenarrable

Learned borrowing from French inénarrable, from Latin inēnārrābilis (“indescribable”), from in- (prefix meaning ‘not’) + ēnārrābilis (“describable, explainable”). Ēnārrābilis is derived from ēnārrāre + -bilis (suffix forming adjectives indicating a capacity or worth of being acted upon); ēnārrāre is the present active infinitive of ēnārrō (“to explain in detail, expound”), from ē- (a variant of ex- (prefix meaning ‘away; out; thoroughly’)) + narrō (“to say; to relate, tell; to describe; to recount, report”) (ultimately from Proto-Indo-European *ǵneh₃- (“to know”)). The English word is analysable as in- + enarrable. Compare ignorant and -able for the components.

来源：wiktionary