The Collaborative International Dictionary of English v.0.48:

Turtle \Tur"tle\ (t[^u]r"t'l), n. [AS. turtle, L. turtur;
   probably of imitative origin. Cf. Turtle the sea tortoise.]
   (Zool.)
   The turtledove.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Turtle \Tur"tle\, n. [Probably the same word as the word
   preceding, and substituted (probably by sailors) for the
   Spanish or Portuguese name; cf. Sp. tortuga tortoise, turtle,
   Pg. tartaruga, also F. tortue, and E. tortoise.]
   [1913 Webster]
   [1913 Webster]
   1. (Zool.) Any one of the numerous species of Testudinata,
      especially a sea turtle, or chelonian.
      [1913 Webster]

   Note: In the United States the land and fresh-water tortoises
         are also called turtles.
         [1913 Webster]

   2. (Printing) The curved plate in which the form is held in a
      type-revolving cylinder press.
      [1913 Webster]

   Alligator turtle, Box turtle, etc. See under Alligator,
      Box, etc.

   green turtle (Zool.), a marine turtle of the genus
      Chelonia, having usually a smooth greenish or
      olive-colored shell. It is highly valued for the delicacy
      of its flesh, which is used especially for turtle soup.
      Two distinct species or varieties are known; one of which
      (Chelonia Midas) inhabits the warm part of the Atlantic
      Ocean, and sometimes weighs eight hundred pounds or more;
      the other (Chelonia virgata) inhabits the Pacific Ocean.
      Both species are similar in habits and feed principally on
      seaweed and other marine plants, especially the turtle
      grass.

   Turtle cowrie (Zool.), a large, handsome cowrie (Cypraea
      testudinaria); the turtle-shell; so called because of its
      fancied resemblance to a tortoise in color and form.

   Turtle grass (Bot.), a marine plant (Thalassia
      testudinum) with grasslike leaves, common about the West
      Indies.

   Turtle shell, tortoise shell. See under Tortoise.
      [1913 Webster]

WordNet (r) 3.0 (2006):

turtle
    n 1: a sweater or jersey with a high close-fitting collar [syn:
         turtleneck, turtle, polo-neck]
    2: any of various aquatic and land reptiles having a bony shell
       and flipper-like limbs for swimming
    v 1: overturn accidentally; "Don't rock the boat or it will
         capsize!" [syn: capsize, turtle, turn turtle]
    2: hunt for turtles, especially as an occupation