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.]
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   1. (Zool.) Any one of the numerous species of Testudinata,
      especially a sea turtle, or chelonian.
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   Note: In the United States the land and fresh-water tortoises
         are also called turtles.
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   2. (Printing) The curved plate in which the form is held in a
      type-revolving cylinder press.
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   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.
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