Source : Webster's Revised Unabridged Dictionary (1913)

Worm \Worm\ (w[^u]rm), n. [OE. worm, wurm, AS. wyrm; akin to D.
   worm, OS. & G. wurm, Icel. ormr, Sw. & Dan. orm, Goth.
   wa['u]rms, L. vermis, Gr. ? a wood worm. Cf. {Vermicelli},
   {Vermilion}, {Vermin}.]
   1. A creeping or a crawling animal of any kind or size, as a
      serpent, caterpillar, snail, or the like. [Archaic]

            There came a viper out of the heat, and leapt on his
            hand. When the men of the country saw the worm hang
            on his hand, they said, This man must needs be a
            murderer.                             --Tyndale
                                                  (Acts xxviii.
                                                  3, 4).

            'T is slander, Whose edge is sharper than the sword,
            whose tongue Outvenoms all the worms of Nile.
                                                  --Shak.

            When Cerberus perceived us, the great worm, His
            mouth he opened and displayed his tusks.
                                                  --Longfellow.

   2. Any small creeping animal or reptile, either entirely
      without feet, or with very short ones, including a great
      variety of animals; as, an earthworm; the blindworm.
      Specifically: (Zo["o]l.)
      (a) Any helminth; an entozo["o]n.
      (b) Any annelid.
      (c) An insect larva.
      (d) pl. Same as {Vermes}.

   3. An internal tormentor; something that gnaws or afflicts
      one's mind with remorse.

            The worm of conscience still begnaw thy soul!
                                                  --Shak.

   4. A being debased and despised.

            I am a worm, and no man.              --Ps. xxii. 6.

   5. Anything spiral, vermiculated, or resembling a worm; as:
      (a) The thread of a screw.

                The threads of screws, when bigger than can be
                made in screw plates, are called worms. --Moxon.
      (b) A spiral instrument or screw, often like a double
          corkscrew, used for drawing balls from firearms.
      (c) (Anat.) A certain muscular band in the tongue of some
          animals, as the dog; the lytta. See {Lytta}.
      (d) The condensing tube of a still, often curved and wound
          to economize space. See Illust. of {Still}.
      (e) (Mach.) A short revolving screw, the threads of which
          drive, or are driven by, a worm wheel by gearing into
          its teeth or cogs. See Illust. of {Worm gearing},
          below.

   {Worm abscess} (Med.), an abscess produced by the irritation
      resulting from the lodgment of a worm in some part of the
      body.

   {Worm fence}. See under {Fence}.

   {Worm gear}. (Mach.)
      (a) A worm wheel.
      (b) Worm gearing.

   {Worm gearing}, gearing consisting of a worm and worm wheel
      working together.

   {Worm grass}. (Bot.)
      (a) See {Pinkroot}, 2
      (a) .
      (b) The white stonecrop ({Sedum album}) reputed to have
          qualities as a vermifuge. --Dr. Prior.

   {Worm oil} (Med.), an anthelmintic consisting of oil obtained
      from the seeds of {Chenopodium anthelminticum}.

   {Worm powder} (Med.), an anthelmintic powder.

   {Worm snake}. (Zo["o]l.) See {Thunder snake}
      (b), under {Thunder}.

   {Worm tea} (Med.), an anthelmintic tea or tisane.

   {Worm tincture} (Med.), a tincture prepared from dried
      earthworms, oil of tartar, spirit of wine, etc. [Obs.]

   {Worm wheel}, a cogwheel having teeth formed to fit into the
      spiral spaces of a screw called a worm, so that the wheel
      may be turned by, or may turn, the worm; -- called also
      {worm gear}, and sometimes {tangent wheel}. See Illust. of
      {Worm gearing}, above.

Source : WordNet®

worm wheel
     n : gear with the thread of a worm