IPA: //ˈɡrʌbiər//
KK: /ˈgrʌbiər/
More dirty or unclean than something else.
After playing outside all day, my clothes were grubbier than before.
Comparative: grubbier
Superlative: grubbiest
Grubbier is formed from "grubby" (from Middle English "grubbe", meaning dirty or soiled) and the comparative suffix "-ier" (meaning more). The word "grubbier" means more dirty or soiled than something else.
Think of something that is 'more dirty' ('grubby') when you add '-ier' to it, which helps you remember that 'grubbier' means dirtier.