The Collaborative International Dictionary of English v.0.48:

Tortoise \Tor"toise\, n. [OE. tortuce, fr. OF. tortis crooked,
   fr. L. tortus twisted, crooked, contorted, p. p. of torquere,
   tortum, to wind; cf. F. tortue tortoise, LL. tortuca,
   tartuca, Pr. tortesa crookedness, tortis crooked. so called
   in allusion to its crooked feet. See Torture.]
   1. (Zool.) Any one of numerous species of reptiles of the
      order Testudinata.
      [1913 Webster]

   Note: The term is applied especially to the land and
         fresh-water species, while the marine species are
         generally called turtles, but the terms tortoise and
         turtle are used synonymously by many writers. See
         Testudinata, Terrapin, and Turtle.
         [1913 Webster]

   2. (Rom. Antiq.) Same as Testudo, 2.
      [1913 Webster]

   Box tortoise, Land tortoise, etc. See under Box,
      Land, etc.

   Painted tortoise. (Zool.) See Painted turtle, under
      Painted.

   Soft-shell tortoise. (Zool.) See Trionyx.

   Spotted tortoise. (Zool.) A small American fresh-water
      tortoise (Chelopus guttatus or Nanemys guttatus)
      having a blackish carapace on which are scattered round
      yellow spots.

   Tortoise beetle (Zool.), any one of numerous species of
      small tortoise-shaped beetles. Many of them have a
      brilliant metallic luster. The larvae feed upon the leaves
      of various plants, and protect themselves beneath a mass
      of dried excrement held over the back by means of the
      caudal spines. The golden tortoise beetle (Cassida
      aurichalcea) is found on the morning-glory vine and
      allied plants.

   Tortoise plant. (Bot.) See Elephant's foot, under
      Elephant.

   Tortoise shell, the substance of the shell or horny plates
      of several species of sea turtles, especially of the
      hawkbill turtle. It is used in inlaying and in the
      manufacture of various ornamental articles.

   Tortoise-shell butterfly (Zool.), any one of several
      species of handsomely colored butterflies of the genus
      Aglais, as Aglais Milberti, and Aglais urticae, both
      of which, in the larva state, feed upon nettles.

   Tortoise-shell turtle (Zool.), the hawkbill turtle. See
      Hawkbill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tortoise
    n 1: usually herbivorous land turtles having clawed elephant-
         like limbs; worldwide in arid area except Australia and
         Antarctica

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "tortoise":
   alligator, crocodile, crocodilian, dawdle, dawdler, dinosaur,
   drone, foot-dragger, gator, goldbrick, goof-off, laggard, lie-abed,
   lingerer, lizard, loiterer, plodder, procrastinator, reptile,
   reptilian, saurian, sleepyhead, slow goer, slow-foot, slowbelly,
   slowpoke, slug, sluggard, snail, stick-in-the-mud, terrapin,
   turtle



Easton's 1897 Bible Dictionary:

Tortoise
   (Heb. tsabh). Ranked among the unclean animals (Lev. 11:29).
   Land tortoises are common in Syria. The LXX. renders the word by
   "land crocodile." The word, however, more probably denotes a
   lizard, called by the modern Arabs _dhabb_.


The Devil's Dictionary (1881-1906):

TORTOISE, n.  A creature thoughtfully created to supply occasion for
the following lines by the illustrious Ambat Delaso:

                          TO MY PET TORTOISE

    My friend, you are not graceful -- not at all;
    Your gait's between a stagger and a sprawl.

    Nor are you beautiful:  your head's a snake's
    To look at, and I do not doubt it aches.

    As to your feet, they'd make an angel weep.
    'Tis true you take them in whene'er you sleep.

    No, you're not pretty, but you have, I own,
    A certain firmness -- mostly you're [sic] backbone.

    Firmness and strength (you have a giant's thews)
    Are virtues that the great know how to use --

    I wish that they did not; yet, on the whole,
    You lack -- excuse my mentioning it -- Soul.

    So, to be candid, unreserved and true,
    I'd rather you were I than I were you.

    Perhaps, however, in a time to be,
    When Man's extinct, a better world may see

    Your progeny in power and control,
    Due to the genesis and growth of Soul.

    So I salute you as a reptile grand
    Predestined to regenerate the land.

    Father of Possibilities, O deign
    To accept the homage of a dying reign!

    In the far region of the unforeknown
    I dream a tortoise upon every throne.

    I see an Emperor his head withdraw
    Into his carapace for fear of Law;

    A King who carries something else than fat,
    Howe'er acceptably he carries that;

    A President not strenuously bent
    On punishment of audible dissent --

    Who never shot (it were a vain attack)
    An armed or unarmed tortoise in the back;

    Subject and citizens that feel no need
    To make the March of Mind a wild stampede;

    All progress slow, contemplative, sedate,
    And "Take your time" the word, in Church and State.

    O Tortoise, 'tis a happy, happy dream,
    My glorious testudinous regime!

    I wish in Eden you'd brought this about
    By slouching in and chasing Adam out.