Also called cinder. the more or less completely fused and vitrified matter separated during the reduction of a metal from its ore.
the scoria from a volcano.
waste left over after the re-sorting of coal.

verb (used with object), slagged, slag·ging.

to convert into slag.
Metallurgy. to remove slag from (a steel bath).

verb (used without object), slagged, slag·ging.

to form slag; become a slaglike mass.

Origin of slag

1545–55; < Middle Low German slagge; cognate with German Schlacke dross, slag; see slack2
Related formsslag·a·ble, adjectiveslag·a·bil·i·ty, nounslag·less, adjectiveslag·less·ness, nounun·slagged, adjective




British Slang. an abusive woman.

Origin of slag

First recorded in 1780–90; originally an argot word for a worthless person or a thug; perhaps identical with slag1 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for slag

lava, residue, refuse, ashes, dross, scoria, cinders, recrement

Examples from the Web for slag

Contemporary Examples of slag

Historical Examples of slag

  • The separation of the slag and iron is facilitated by throwing in some lime from time to time.

  • Of these, oyster or marine shells, burnt shale, and slag are most common.

  • Because, at the foot of the tree, as if broken off the stone, fragments of slag were found.

  • This cement is made of limestone and clay, or marl, chalk, and slag.

    Diggers in the Earth

    Eva March Tappan

  • Slag and sand were delivered to the mixer by means of wheelbarrows.

    Concrete Construction

    Halbert P. Gillette

British Dictionary definitions for slag



Also called: cinder the fused material formed during the smelting or refining of metals by combining the flux with gangue, impurities in the metal, etc. It usually consists of a mixture of silicates with calcium, phosphorus, sulphur, etcSee also basic slag
a mass of rough fragments of pyroclastic rock and cinders derived from a volcanic eruption; scoria
a mixture of shale, clay, coal dust, and other mineral waste produced during coal mining
British slang a coarse or dissipated girl or woman

verb slags, slagging or slagged

(tr) British slang (usually foll by off) to abuse (someone) verbally
(intr) Australian slang to spit
Derived Formsslagging, nounslaggy, adjective

Word Origin for slag

C16: from Middle Low German slagge, perhaps from slagen to slay
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for slag

"refuse from smelting," 1550s, from Middle Low German slagge (German Schlacke) "splinter flying off when metal is struck," related to Old High German slahan "to strike, slay" (see slay (v.)).


"denigrate," by 1971, from slag (n.) in a secondary sense of "worthless person" (1788). Related: Slagged; slagging.

Online Etymology Dictionary, © 2010 Douglas Harper

slag in Science



The vitreous mass left as a residue by the smelting of metallic ore. It consists mostly of the siliceous and aluminous impurities from the iron ore.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.