Source : Webster's Revised Unabridged Dictionary (1913)

Cooter \Coot"er\ (-[~e]r), n. (Zo["o]l.)
      (a) A fresh-water tortoise ({Pseudemus concinna}) of
          Florida.
      (b) The box tortoise.

Source : WordNet®

cooter
     n : large river turtle of the southern United States and
         northern Mexico [syn: {river cooter}, {Pseudemys concinna}]