late 14c., "covered with slime; of the nature of slime," from slime (n.) + -y (2). Similar formation in Middle Dutch slimich, Dutch slijmig, German schleimig. Figurative sense of "morally repulsive" is first attested 1570s. Related: Slimily; sliminess.[slimy etymology, slimy origin, 英语词源]