Soot

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Old English sōt, of Germanic origin; related to German dialect Sott, from an Indo-European root shared by the verb sit.

wiktionary

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From Middle English soot, soote, sote, sot, from Old English sōt [1], from Proto-Germanic *sōtą(“soot”), from Proto-Indo-European *sed-(“to sit”). Cognate with dated Dutch zoet(“soot”), German Low German Soot(“soot”), Danish sod(“soot”), Swedish sot(“soot”), Icelandic sót(“soot”). Compare similar ō-grade formation the same Proto-Indo-European root in Old Irish suide(“soot”) and Balto-Slavic: Lithuanian súodžiai(“soot”), and Proto-Slavic *saďa(“soot”) (Russian са́жа(sáža), Polish and Slovak sadza, Bulgarian са́жда(sážda)).

etymonline

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soot (n.)

Old English sot "soot," from Proto-Germanic *sotam "soot" (source also of Old Norse sot, Old Dutch soet, North Frisian sutt), literally "what settles," from PIE *sodo- (source also of Old Church Slavonic sažda, Lithuanian suodžiai, Old Irish suide, Breton huzel "soot"), suffixed form of root *sed- (1) "to sit."