Soot is the fine black powder left behind by smoke. It settles on everything and gets under your fingernails.
It is unburnt carbon, produced whenever fuel does not burn cleanly, which is why chimneys need sweeping and why candles blacken a ceiling. It is genuinely harmful to breathe, and soot in the air is a large part of what makes urban pollution dangerous. The adjective is sooty. The trade of sweeping it out gave English the chimney sweep, and Victorian London ran on the stuff.
1nounsootThe fine black powder deposited by smoke.
“Soot had built up inside the flue.”
Proto-Indo-European
*sed- — to sit
Proto-Germanic
*sōtą — soot
Old English
sōt
Middle English
soot,soote,sote,sot
English, today
soot
Middle English soot,soote,sote,sot, from Old English sōt, 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”), Norwegian Bokmål, Norwegian Nynorsk and Swedish sot (“soot”), Icelandic sót (“soot”). Compare similar ō-grade formation the same Proto-Indo-European root in Old Irish suide (“soot”) and ine-bsl: Lithuanian súodžiai (“soot”), and Proto-Slavic saďa (“soot”) (Russian са́жа, Polish - and Slovak sadza, Bulgarian са́жда).
Etymology from Wiktionary, CC BY-SA