The word "befouls" means to make something dirty or polluted. Antonyms for this word would include words like "cleanse," "purify," "sanitize," "disinfect," or "sterilize." These opposite words all suggest the idea of removing impurities or contaminants from something. For example, cleansing a wound or purifying water. Other words that could act as antonyms for "befouls" include "polish" or "sharpen," suggesting a process of making something brighter, sharper, or more refined. Overall, the antonyms for "befouls" are words that describe processes of cleaning, purifying, and improving the quality of something.