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.

2. That which is expanded; expanse; extend surface; as, the expansion of a sheet or of a lake; the expansion was formed of metal.

The starred expansion of the skies. --Beattie.

3. Space through which anything is expanded; also, pure space.

Lost in expansion, void and infinite. --Blackmore.

4. (Com.) Enlargement or extension of business transactions; esp., increase of the circulation of bank notes.

5. (Math.) The developed result of an indicated operation; as, the expansion of (a + b)^2 is a^2 + 2ab + b^2.

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.

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.

Note: Expansion is also used adjectively, as in expansion joint, expansion gear, etc.

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 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 by heat, is prevented from causing injurious strains; as:
   (a) A side 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.

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

Source: Webster's Revised Unabridged Dictionary (1913)
 

Gear \Gear\, n. [OE. gere, ger, AS. gearwe clothing, adornment, armor, fr. gearo, gearu, ready, yare; akin to OHG. garaw[=i], garw[=i] ornament, dress. See Yare, and cf. Garb dress.]

1. Clothing; garments; ornaments.

Array thyself in thy most gorgeous gear. --Spenser.

2. Goods; property; household stuff. --Chaucer.

Homely gear and common ware. --Robynson (More's Utopia).

3. Whatever is prepared for use or wear; manufactured stuff or material.

Clad in a vesture of unknown gear. --Spenser.

4. The harness of horses or cattle; trapping.

5. Warlike accouterments. [Scot.]

--Jamieson.

6. Manner; custom; behavior. [Obs.]

--Chaucer.

7. Business matters; affairs; concern. [Obs.]

Thus go they both together to their gear. --Spenser.

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.

9. pl. (Naut.) See 1st Jeer
   (b) .

10. Anything worthless; stuff; nonsense; rubbish. [Obs. or Prov. Eng.]

--Wright.

That servant of his that confessed and uttered this gear was an honest man. --Latimer.

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, or out of, gear (Mach.), to connect or disconnect (wheelwork or couplings, etc.); to put in, or out of, working relation.

Source: Webster's Revised Unabridged Dictionary (1913)