Adynaton (/ˌædɪˈnɑːtɒn, -tən/;[1] plural adynata) is a figure of speech in the form of hyperbole taken to such extreme lengths as to insinuate a complete impossibility:[2]
I will sooner have a beard grow in the palm of my hand than he shall get one on his cheek.[3]
The word derives from the Greek ἀδύνατον (adunaton), neuter of ἀδύνατος (adunatos), "unable, impossible" (a-, "without" + dynasthai, "to be possible or powerful").[4]