1. a flowing or flow.
  2. the flowing in of the tide.
  3. continuous change, passage, or movement: His political views are in a state of flux.
  4. Physics.
    1. the rate of flow of fluid, particles, or energy.
    2. a quantity expressing the strength of a field of force in a given area.
  5. Chemistry, Metallurgy.
    1. a substance used to refine metals by combining with impurities to form a molten mixture that can be readily removed.
    2. a substance used to remove oxides from and prevent further oxidation of fused metal, as in soldering or hot-dip coating.
    3. (in the refining of scrap or other metal) a salt or mixture of salts that combines with nonmetallic impurities, causing them to float or coagulate.
  6. fusion.

verb (used with object)

  1. to melt; make fluid.
  2. to fuse by the use of flux.
  3. Obsolete. to purge.

verb (used without object)

  1. to flow.


  1. a flow or discharge
  2. continuous change; instability
  3. a substance, such as borax or salt, that gives a low melting-point mixture with a metal oxide. It is used for cleaning metal surfaces during soldering, etc, and for protecting the surfaces of liquid metals
  4. metallurgy a chemical used to increase the fluidity of refining slags in order to promote the rate of chemical reaction
  5. a similar substance used in the making of glass
  6. physics
    1. the rate of flow of particles, energy, or a fluid, through a specified area, such as that of neutrons (neutron flux) or of light energy (luminous flux)
    2. the strength of a field in a given area expressed as the product of the area and the component of the field strength at right angles to the areamagnetic flux; electric flux
  7. pathol an excessive discharge of fluid from the body, such as watery faeces in diarrhoea
  8. the act or process of melting; fusion
  9. (in the philosophy of Heraclitus) the state of constant change in which all things exist


  1. to make or become fluid
  2. (tr) to apply flux to (a metal, soldered joint, etc)
  3. (tr) an obsolete word for purge

late 14c., from Old French flus “flowing, rolling, bleeding,” or directly from Latin fluxus “flowing, loose, slack,” past participle of fluere “to flow” (see fluent). Originally “excessive flow” (of blood or excrement); an early name for “dysentery;” sense of “continuous succession of changes” is first recorded 1620s. The verb is early 15c., from the noun.


  1. The discharge of large quantities of fluid material from the body, especially the discharge of watery feces from the intestines.
  2. Material thus discharged from the bowels.
  3. The rate of flow of fluid, particles, or energy through a given surface.
  4. Flux density.

  1. The rate of flow of fluids, particles, or energy across a given surface or area.
  2. The presence of a field of force in a region of space, represented as a set of lines indicating the direction of the force. The density of the lines indicates the strength of the force. Lines used to represent magnetic fields in depictions of magnets, for example, follow the lines of flux of the field. See also field magnetic flux.
  3. A measure of the strength of such a field.
  4. A readily fusible glass or enamel used as a base in ceramic work.
  5. An additive that improves the flow of plastics during fabrication.
  6. A substance applied to a surface to be joined by welding, soldering, or brazing to facilitate the flowing of solder and prevent formation of oxides.
  7. A substance used in a smelting furnace to make metals melt more easily.
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