slag

¹ American  

[slag] / slæg /

noun

1. Also called cinder.  the more or less completely fused and vitrified matter separated during the reduction of a metal from its ore.

2. the scoria from a volcano.

3. waste left over after the re-sorting of coal.

---

verb (used with object)

slagged, slagging

1. to convert into slag.

2. Metallurgy. to remove slag from (a steel bath).

verb (used without object)

slagged, slagging

1. to form slag; become a slaglike mass.

slag ² American  

[slag] / slæg /

noun

1. British Slang. an abusive woman.

---

slag British  

/ slæɡ /

noun

1. 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, etc See also basic slag

2. a mass of rough fragments of pyroclastic rock and cinders derived from a volcanic eruption; scoria

3. a mixture of shale, clay, coal dust, and other mineral waste produced during coal mining

4. slang a coarse or dissipated girl or woman

---

verb

1. slang (tr) (usually foll by off) to abuse (someone) verbally

2. slang (intr) to spit

slag Scientific  

/ slăg /

1. 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.

---

Usage

What else does slag mean? Content warning: the following content includes references to strong and sexist language. In slang, slag is an insulting British English term for a contemptible person. When used of women, it can be equivalent to slut. As a verb, to slag (off somebody) is "to attack (them) verbally," i.e., to talk smack about them.

Other Word Forms

• slagability
  noun
• slagging
  noun
• slaglessness
  noun
• slagable
  adjective
• slaggy
  adjective
• slagless
  adjective
• unslagged
  adjective

Etymology

Origin of slag¹

1545–55; < Middle Low German slagge; cognate with German Schlacke dross, slag; see slack ²

Origin of slag²

First recorded in 1780–90; originally an argot word for a worthless person or a thug; perhaps identical with slag ¹

Example Sentences

Copper, steel, aluminum and precious metals can be recovered, but rare-earth metals typically fuse with other byproducts in waste called slag.

From The Wall Street Journal • Jan. 23, 2026

“There were high concentrations of slag in these, which is a glass-like material that makes them maybe a little bit more brittle in the cold,” she says.

From BBC • Aug. 13, 2024

The Cambridge team spotted the composition of used cement is almost exactly the same as the slag used in electric arc furnaces.

From BBC • May 22, 2024

"We found the combination of cement clinker and iron oxide is an excellent steelmaking slag because it foams and it flows well," said Dunant.

From Science Daily • May 22, 2024

On Warren’s bulletin board she spotted the photo from her art school application: the etched-in image of the two of them, children, climbing up the mountain of slag.

From "Little Fires Everywhere" by Celeste Ng

Related Words

• lava