adynaton

Borrowed from Late Latin adynaton (“impossibility; adynaton”), or directly from its etymon Ancient Greek ἀδύνατον (adúnaton, “an impossibility; impracticality”), substantivized neuter singular of ἀδύνατος (adúnatos, “unable; that cannot be done, impossible”) + -ον (-on, suffix forming nouns). The word ἀδύνατος is derived from ἀ- (a-, the alpha privative, a prefix forming words having a sense opposite to the word or stem to which it is attached) + δῠνᾰτός (dŭnătós, “mighty, strong; possible, practical”) (from δῠ́νᾰμαι (dŭ́nămai, “to be able, capable; it can be, it is possible”) (from Proto-Indo-European *dewh₂- (“to fit”)) + -τος (-tos, suffix forming verbal adjectives of possibility)).

来源：wiktionary