Adynaton (noun)
ad-in-a-ton
A figure of speech in the form of hyperbole taken to such extreme lengths as to insinuate a complete impossibility
The word derives from the Greek ἀδύνατον (adunaton), neuter of ἀδύνατος (adunatos), “unable, impossible” (a-, “without” + dynasthai, “to be possible or powerful”)
Example sentences
“He was fond of an adynaton, once claiming that he will sooner have a beard grow in the palm of my hand than he shall get one on his face.”