IPA: /ɡrɪmər/
KK: /ˈgrɪmɚ/
More serious, harsh, or gloomy than something else.
The news about the storm was grimmer than we expected.
Grimmer is derived from the comparative form of the adjective "grim" (from Old English *grim*, meaning fierce or cruel). The suffix "-er" indicates a comparative degree. Therefore, "grimmer" means more grim or more fierce than something else.
Think of the word 'grim' which means fierce or cruel, and remember that 'grimmer' means more fierce or more cruel.