What is "worm gear"

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.)

   1. Any helminth; an entozo["o]n.

   2. Any annelid.

   3. An insect larva.

   4. 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:

   1. The thread of a screw.

      The threads of screws, when bigger than can be made in screw plates, are called worms.
      --Moxon.

   2. A spiral instrument or screw, often like a double corkscrew, used for drawing balls from firearms.

   3. (Anat.) A certain muscular band in the tongue of some animals, as the dog; the lytta. See Lytta.

   4. The condensing tube of a still, often curved and wound to economize space. See Illust. of Still.

   5. (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.)

      1. A worm wheel.

      2. Worm gearing. Worm gearing, gearing consisting of a worm and worm wheel working together. Worm grass. (Bot.)

         1. See Pinkroot, 2 (a) .

         2. 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.

n. gear consisting of a shaft with screw thread (the worm) that meshes with a toothed wheel (the worm wheel); changes the direction of the axis of rotary motion