flux / fləks/ • n. 1. the action or process of flowing or flowing out: the flux of men and women moving back and forth | a localized flux of calcium into the cell. ∎  Med. an abnormal discharge of blood or other matter from or within the body. ∎  (usu. the flux) archaic diarrhea or dysentery.2. continuous change: the whole political system is in a state of flux.3. Physics the rate of flow of a fluid, radiant energy, or particles across a given area. ∎  the amount of radiation or number of particles incident on an area in a given time. ∎  the total electric or magnetic field passing through a surface.4. a substance mixed with a solid to lower its melting point, used esp. in soldering and brazing metals or to promote vitrification in glass or ceramics. ∎  a substance added to a furnace during metal smelting or glassmaking that combines with impurities to form slag.• v. [tr.] treat (a metal object) with a flux to promote melting.

flux In ceramics, any substance that promotes vitrification when mixed with clay. When the ware is fired, the flux melts, filling the porous clay form. As the piece cools, it hardens, becoming glossy and non-porous. Fluxes include felspathic rock, silica and borax. In metallurgy, a flux is added to the charge of a smelting furnace to purge impurities from the ore and to lower the melting point of the slag.

flux copious flowing of blood, etc. XIV; (gen.) flowing; continuous succession XVI; incoming tide, opp. of reflux XVII; substance facilitating fusion (earlier †fluss — G.) XVIII. In early use (XIV–XVII) also †flix — (O)F. flux or L. fluxus, f. fluere flow.
So fluxion †flow, flowing XVI; (math.) rate of change of a continuously varying quantity XVIII.

flux (fluks) n. an abnormally copious flow from an organ or cavity.