IPA: /ˈfaʊlɪst/
KK: /faʊlɪst/
The most unpleasant or offensive in smell, taste, or behavior.
The foulest smell came from the garbage can that hadn't been emptied for weeks.
Comparative: fouler
Superlative: foulest
Foulest → It is formed from "foul" (from Old English *fūl*, meaning offensive or unpleasant) and the superlative suffix "-est" (meaning most). The word "foulest" means the most offensive or unpleasant.
Think of the Old English word for offensive or unpleasant, 'foul', and remember that 'foulest' means the most foul or the worst in terms of unpleasantness.