Etymology: < Middle Low German slagge, either (i) < slag- , stem of slān to forge, work metal (specific use of slān to strike, to beat: see slay v.¹) + a suffix forming nouns (taken to have originally referred to waste generated by forging metal rather than smelting ore), or perhaps (ii) < the same base as Middle Low German slagge rainy or dirty weather (see slag adj.). Compare ( < Middle Low German slagge slag) Old Swedish slag (Swedish slagg) and German Schlacke, †Schlack (16th cent.).Compare the independently-formed Old English (Mercian) slægu (reflecting earlier *slagu , after Second Fronting of a to æ ), attested in glossaries, rendering post-classical Latin lihargum , apparently an error for an inflected form of classical Latin lithargyrus litharge n., denoting lead monoxide or a similar substance (perhaps including white lead, which can be present in slag from lead smelting; compare litharge n. 2). The antecedent Old English *slagu is perhaps the same word as slagu blow, stroke (in mān-slagu wicked blow, morþor-slagu homicide), cognate with Middle Dutch slāge slaughterhouse, plague, disaster, Old Saxon slaga (in hōf-slaga hoofbeat; Middle Low German slāge hammer, track, trace, barrier), Old High German slaga hammer, sledgehammer, blow (Middle High German slage , German regional Schlage hammer) < the same Germanic base as slay v.¹ If slag n.¹ is related to words for wet matter (see derivation (ii) above and compare slag adj.), perhaps compare Scots slag blob, wet mass, messy mouthful of food, dollop (18th cent.), especially given the blob-like appearance of larger pieces of slag, resulting from bubbles formed in the smelting process.

Etymology: Probably an alteration of slang n.⁴, perhaps after slag n.¹

Etymology: Probably < early Scandinavian (compare Old Norwegian slag hard, heavy rain, water penetrating walls (Norwegian (Nynorsk) slagg slaver), Old Swedish slag sleet (Swedish slagg )) < the same Germanic base as (with different stem class) Middle Low German slagge rainy or dirty weather, Old Icelandic slagi dampness, perhaps related to the Germanic base of slough n.¹ Further etymology. For phonological reasons, the Germanic base cannot be cognate with Russian sljakot′ , Polish śląkwa , both in the senses ‘rainy weather, wet snow, slush’, Lithuanian šlakas drop, freckle, spot, Latvian slaka drop, sprinkle, moistening. It has, however, been suggested that the Germanic and Balto-Slavonic words may reflect borrowings ultimately < the same non-Indo-European substrate language. Comments on the Scandinavian etymon. The Scandinavian word appears to have been a noun originally, and the apparent use as adjective (in English) may have developed from an attributive use of the noun, modifying another noun (in either language). It has been suggested that the Scandinavian word shows a specific use of the word for a blow or stroke reflected in Old Icelandic slag (compare the forms cited at slay n.¹); this poses formal and semantic problems, but there may have been some folk-etymological association of the two words. Modern parallels. Compare also Scots (southern) slag (noun) marshy place, morass (1802) and also the derivative adjective slaggie, designating the quality of the ice during a thaw, and the compound slag-day, denoting a day on which ice is thawing (both 1824), and also Shetland Scots slag (noun) hollow in the ground (especially a muddy one), soft sea bed (in a fishing ground), all ultimately reflecting separate borrowings of the same or a related word in a Scandinavian language.

Etymology: < slag n.¹With sense 2 perhaps compare earlier slang v. 4.