The Collaborative International Dictionary of English v.0.48:

Gear \Gear\ (g[=e]r), n. [OE. gere, ger, AS. gearwe clothing,
   adornment, armor, fr. gearo, gearu, ready, yare; akin to OHG.
   garaw[imac], garw[imac] ornament, dress. See Yare, and cf.
   Garb dress.]
   1. Clothing; garments; ornaments.
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            Array thyself in thy most gorgeous gear. --Spenser.
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   2. Goods; property; household stuff. --Chaucer.
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            Homely gear and common ware.          --Robynson
                                                  (More's
                                                  Utopia).
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   3. Whatever is prepared for use or wear; manufactured stuff
      or material.
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            Clad in a vesture of unknown gear.    --Spenser.
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   4. The harness of horses or cattle; trapping.
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   5. Warlike accouterments. [Scot.] --Jamieson.
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   6. Manner; custom; behavior. [Obs.] --Chaucer.
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   7. Business matters; affairs; concern. [Obs.]
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            Thus go they both together to their gear. --Spenser.
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   8. (Mech.)
      (a) A toothed wheel, or cogwheel; as, a spur gear, or a
          bevel gear; also, toothed wheels, collectively.
      (b) An apparatus for performing a special function;
          gearing; as, the feed gear of a lathe.
      (c) Engagement of parts with each other; as, in gear; out
          of gear.
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   9. pl. (Naut.) See 1st Jeer
      (b) .
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   10. Anything worthless; stuff; nonsense; rubbish. [Obs. or
       Prov. Eng.] --Wright.
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             That servant of his that confessed and uttered this
             gear was an honest man.              --Latimer.
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   Bever gear. See Bevel gear.

   Core gear, a mortise gear, or its skeleton. See Mortise
      wheel, under Mortise.

   Expansion gear (Steam Engine), the arrangement of parts for
      cutting off steam at a certain part of the stroke, so as
      to leave it to act upon the piston expansively; the
      cut-off. See under Expansion.

   Feed gear. See Feed motion, under Feed, n.

   Gear cutter, a machine or tool for forming the teeth of
      gear wheels by cutting.

   Gear wheel, any cogwheel.

   Running gear. See under Running.

   To throw in gear or To throw out of gear (Mach.), to
      connect or disconnect (wheelwork or couplings, etc.); to
      put in, or out of, working relation.
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The Collaborative International Dictionary of English v.0.48:

Expansion \Ex*pan"sion\, n. [L. expansio: cf. F. expansion.]
   1. The act of expanding or spreading out; the condition of
      being expanded; dilation; enlargement.
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   2. That which is expanded; expanse; extend surface; as, the
      expansion of a sheet or of a lake; the expansion was
      formed of metal.
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            The starred expansion of the skies.   --Beattie.
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   3. Space through which anything is expanded; also, pure
      space.
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            Lost in expansion, void and infinite. --Blackmore.
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   4. (Economics & Commmerce) an increase in the production of
      goods and services over time, and in the volume of
      business transactions, generally associated with an
      increase in employment and an increase in the money
      supply. Opposite of contraction.

   Syn: economic expansion. [1913 Webster +PJC]

   5. (Math.) The developed result of an indicated operation;
      as, the expansion of (a + b)^2 is a^2 + 2ab + b^2.
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   6. (Steam Engine) The operation of steam in a cylinder after
      its communication with the boiler has been cut off, by
      which it continues to exert pressure upon the moving
      piston.
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   7. (Nav. Arch.) The enlargement of the ship mathematically
      from a model or drawing to the full or building size, in
      the process of construction. --Ham. Nav. Encyc.
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   Note: Expansion is also used adjectively, as in expansion
         joint, expansion gear, etc.
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   8. an enlarged or extended version of something, such as a
      writing or discourse; as, the journal article is an
      expansion of the lecture she gave.
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   9. an expansion joint. See below. [Colloq. or jargon]
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   Expansion curve, a curve the co["o]rdinates of which show
      the relation between the pressure and volume of expanding
      gas or vapor; esp. (Steam engine), that part of an
      indicator diagram which shows the declining pressure of
      the steam as it expands in the cylinder.

   Expansion gear (Steam Engine). a cut-off gear. See Illust.
      of Link motion.

   Automatic expansion gear or Automatic cut-off, one that
      is regulated by the governor, and varies the supply of
      steam to the engine with the demand for power.

   Fixed expansion gear, or Fixed cut-off, one that always
      operates at the same fixed point of the stroke.

   Expansion joint, or Expansion coupling (Mech. & Engin.),
      a yielding joint or coupling for so uniting parts of a
      machine or structure that expansion, as by heat, is
      prevented from causing injurious strains; as:
      (a) A slide or set of rollers, at the end of bridge truss,
          to support it but allow end play.
      (b) A telescopic joint in a steam pipe, to permit one part
          of the pipe to slide within the other.
      (c) A clamp for holding a locomotive frame to the boiler
          while allowing lengthwise motion.
      (d) a strip of compressible material placed at intervals
          between blocks of poured concrete, as in roads or
          sidewalks.

   Expansion valve (Steam Engine), a cut-off valve, to shut
      off steam from the cylinder before the end of each stroke.
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