The Collaborative International Dictionary of English v.0.48:

Sloth \Sloth\, n. [OE. slouthe, sleuthe, AS. sl?w?, fr. sl[=a]w
   slow. See Slow.]
   1. Slowness; tardiness.
      [1913 Webster]

            These cardinals trifle with me; I abhor
            This dilatory sloth and tricks of Rome. --Shak.
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   2. Disinclination to action or labor; sluggishness; laziness;
      idleness.
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            [They] change their course to pleasure, ease, and
            sloth.                                --Milton.
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            Sloth, like rust, consumes faster than labor wears.
                                                  --Franklin.
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   3. (Zool.) Any one of several species of arboreal edentates
      constituting the family Bradypodidae, and the suborder
      Tardigrada. They have long exserted limbs and long
      prehensile claws. Both jaws are furnished with teeth (see
      Illust. of Edentata), and the ears and tail are
      rudimentary. They inhabit South and Central America and
      Mexico.
      [1913 Webster]

   Note: The three-toed sloths belong to the genera Bradypus
         and Arctopithecus, of which several species have been
         described. They have three toes on each foot. The
         best-known species are collared sloth (Bradypus
         tridactylus), and the ai (Arctopitheus ai). The
         two-toed sloths, consisting the genus Cholopus, have
         two toes on each fore foot and three on each hind foot.
         The best-known is the unau (Cholopus didactylus) of
         South America. See Unau. Another species (Cholopus
         Hoffmanni) inhabits Central America.
         Various large extinct terrestrial edentates, such as
         Megatherium and Mylodon, are often called sloths.
         [1913 Webster]

   Australian sloth, or Native sloth (Zool.), the koala.

   Sloth animalcule (Zool.), a tardigrade.

   Sloth bear (Zool.), a black or brown long-haired bear
      (Melursus ursinus, or Melursus labiatus), native of
      India and Ceylon; -- called also aswail, labiated
      bear, and jungle bear. It is easily tamed and can be
      taught many tricks.

   Sloth monkey (Zool.), a loris.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sloth \Sloth\, v. i.
   To be idle. [Obs.] --Gower.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sloth
    n 1: a disinclination to work or exert yourself [syn: sloth,
         slothfulness]
    2: any of several slow-moving arboreal mammals of South America
       and Central America; they hang from branches back downward
       and feed on leaves and fruits [syn: sloth, tree sloth]
    3: apathy and inactivity in the practice of virtue (personified
       as one of the deadly sins) [syn: sloth, laziness,
       acedia]

Moby Thesaurus II by Grady Ward, 1.0:

185 Moby Thesaurus words for "sloth":
   Chiroptera, Lagomorpha, Primates, Rodentia, accidia, acedia,
   aloofness, anger, apathy, army, ataraxia, ataraxy, avarice,
   avaritia, benumbedness, blah, blahs, boredom, bunch, carelessness,
   casualness, cautiousness, cave of Trophonius, cave of despair,
   circumspection, colony, comatoseness, creeping, deadly sin,
   deliberateness, deliberation, despair, desperateness, desperation,
   despondency, detachment, dilatoriness, disconsolateness,
   disinterest, dispassion, disregard, disregardfulness,
   do-nothingness, drawl, drift, drive, drove, drowsiness, dullness,
   easygoingness, enervation, ennui, envy, ergophobia, faineancy,
   faineantise, fatigue, flock, foot-dragging, forlornness, gam, gang,
   gluttony, greed, gula, heartlessness, heaviness, hebetude,
   heedlessness, herd, hoboism, hopelessness, host, idleness, idling,
   inanimation, inappetence, inattention, inattentiveness,
   incuriosity, indifference, indiscrimination, indolence, inertia,
   inertness, inexcitability, inexertion, insouciance, invidia, ira,
   jadedness, just being, kennel, lack of affect, lack of appetite,
   lackadaisicalness, laggardness, languidness, languishment, languor,
   languorousness, lassitude, laze, laziness, lazing, leisureliness,
   lenitude, lentitude, lentor, lethargicalness, lethargy,
   lifelessness, listlessness, litter, loafing, lotus-eating, lust,
   luxuria, mere existence, mere tropism, mindlessness, negligence,
   no exit, no way, no way out, nonchalance, numbness, oscitancy,
   pack, passiveness, passivity, phlegm, phlegmaticalness,
   phlegmaticness, plucklessness, pococurantism, pod, pokiness, pride,
   recklessness, regardlessness, reluctance, remissness, resignation,
   resignedness, satedness, school, shiftlessness, shoal, skulk,
   slackness, sleepiness, slothfulness, slouch, slowness, sluggardy,
   sluggishness, somnolence, sopor, soporifousness, spiritlessness,
   spring fever, spunklessness, stagnation, stupefaction, stupor,
   superbia, supineness, tentativeness, torpidity, torpidness,
   torpitude, torpor, trip, troop, unanxiousness, unconcern,
   unmindfulness, unsolicitousness, vagrancy, vegetation, weariness,
   withdrawnness, world-weariness, wrath