The Collaborative International Dictionary of English v.0.48:

Alligator \Al"li*ga`tor\, n. [Sp. el lagarto the lizard (el
   lagarto de Indias, the cayman or American crocodile), fr. L.
   lacertus, lacerta, lizard. See Lizard.]
   1. (Zool.) A large carnivorous reptile of the Crocodile
      family, peculiar to America. It has a shorter and broader
      snout than the crocodile, and the large teeth of the lower
      jaw shut into pits in the upper jaw, which has no marginal
      notches. Besides the common species of the southern United
      States, there are allied species in South America.
      [1913 Webster]

   2. (Mech.) Any machine with strong jaws, one of which opens
      like the movable jaw of an alligator; as,
      (a) (Metal Working) a form of squeezer for the puddle
          ball.;
      (b) (Mining) a rock breaker;
      (c) (Printing) a kind of job press, called also alligator
          press.
          [1913 Webster]

   Alligator apple (Bot.), the fruit of the Anona palustris,
      a West Indian tree. It is said to be narcotic in its
      properties. --Loudon.

   Alligator fish (Zool.), a marine fish of northwestern
      America (Podothecus acipenserinus).

   Alligator gar (Zool.), one of the gar pikes (Lepidosteus
      spatula) found in the southern rivers of the United
      States. The name is also applied to other species of gar
      pikes.

   Alligator pear (Bot.), a corruption of Avocado pear. See
      Avocado.

   Alligator snapper, Alligator tortoise, Alligator turtle
      (Zool.), a very large and voracious turtle (Macrochelys
      lacertina) inhabiting the rivers of the southern United
      States. It sometimes reaches the weight of two hundred
      pounds. Unlike the common snapping turtle, to which the
      name is sometimes erroneously applied, it has a scaly head
      and many small scales beneath the tail. This name is
      sometimes given to other turtles, as to species of
      Trionyx.

   Alligator wood, the timber of a tree of the West Indies
      (Guarea Swartzii).
      [1913 Webster]

WordNet (r) 3.0 (2006):

alligator snapper
    n 1: large species having three ridges on its back; found in
         southeastern United States [syn: alligator snapping
         turtle, alligator snapper, Macroclemys temmincki]