Answer: sootiest

AnswerCrossword Clue
SOOTIESTMost like a chimney flue
SOOTIESTMost fuliginous
SOOTIESTMost like a chimney sweep
sootiestSOOTY, covered with soot
sootiestconsisting of or resembling soot
sootiestof a black, blackish, or dusky color
sootiestcovered, blackened, or smirched with soot