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.
      [1913 Webster]

   2. Disinclination to action or labor; sluggishness; laziness;
      idleness.
      [1913 Webster]

            [They] change their course to pleasure, ease, and
            sloth.                                --Milton.
      [1913 Webster]

            Sloth, like rust, consumes faster than labor wears.
                                                  --Franklin.
      [1913 Webster]

   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:

Ai \A"i\, n.; pl. Ais. [Braz. a["i], ha["i], from the animal's
   cry: cf. F. a["i].] (Zool.)
   The three-toed sloth (Bradypus tridactylus) of South
   America. See Sloth.
   [1913 Webster] Aiblins

WordNet (r) 3.0 (2006):

Bradypus tridactylus
    n 1: a sloth that has three long claws on each forefoot and each
         hindfoot [syn: three-toed sloth, ai, Bradypus
         tridactylus]