IPA: /ˈɡrɪmiəst/
KK: /ˈɡrɪmaɪst/
The most dirty or covered with grime; very filthy.
After the storm, the streets were the grimiest they had ever been.
Comparative: grimmer
Superlative: grimiest
Grimiest → It is formed from "grimy" (from Middle English "grimy", meaning covered with grime or dirt) and the superlative suffix "-est" (meaning most). The word "grimiest" means the most covered with grime or dirt.
Think of something that is the "most" covered in dirt or filth — that's what "grimiest" means.
No commonly confused words.