soot (n.) Look up soot at Dictionary.com
Old English sot "soot," from Proto-Germanic *sotam "soot" (cognates: Old Norse sot, Old Dutch soet, North Frisian sutt), literally "what settles," from PIE *sod-o- (cognates: Old Church Slavonic sažda, Lithuanian suodžiai, Old Irish suide, Breton huzel "soot"), suffixed form of root *sed- (1) "to sit" (see sedentary).