IPA: /ˈsuːtiːəst/
KK: /ˈsutɪst/
The most covered in soot or dirt, often used to describe something that is very dirty or blackened.
After the fire, the walls were the sootiest they had ever been.
Comparative: sootier
Superlative: sootiest
Sootiests is formed from "soot" (from Old English *sōt*, meaning a black powdery substance produced by burning) and "-iest" (a superlative suffix indicating the highest degree). The word "sootiest" means having the most soot or being the most covered in soot.
Think of the word 'soot' as the black substance from burning, and remember that 'sootiest' means having the most of that black substance.