thiev·ish \ˈthēvish, -vēsh\adjective Etymology: Middle English thevysch, thefyisch, from thef, theef thief + -ysch, -ish -ish 1.obsolete: infested by thieves < bid me … walk in thievish ways — Shakespeare > 2. a.: given to stealing < thievish magpies > b.: of, relating to, or characteristic of a thief : stealthy, sly • thiev·ish·lyadverb • thiev·ish·nessnoun-es