late 12c., "indolence, sluggishness," formed from Middle English slou, slowe (see slow, adj.) + abstract formative -th(2). Replaced Old English slæwð "sloth, indolence." Sense of "slowness, tardiness" is from mid-14c. As one of the deadly sins, it translates Latin accidia.The slow-moving mammal first so called 1610s, a translation of Portuguese preguiça "slowness, slothfulness," from Latin pigritia "laziness" (compare Spanish perezosa "slothful," also "the sloth").