Sloth

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Old English: from slow + -th2.

wiktionary

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From Middle English slouthe, slewthe(“laziness”), from Old English slǣwþ(“sloth, indolence, laziness, inertness, torpor”), from Proto-Germanic *slaiwiþō(“slowness, lateness”), equivalent to slow +‎ -th. Cognate with Scots sleuth(“sloth, slowness”).

etymonline

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sloth (n.)

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").