Negative adverb used before verbs, adjectives, and other adverbs to indicate negation; also used as a bound-form prefix to form terms with opposite meanings

to treat a disease or medical condition; to cure; to wipe out pests or eliminate something harmful

Used in certain constructions to indicate that the second action or state follows immediately from or is the result of the first, as in 一 yī...ér...

(bound form) to recover from an illness; to heal; to get better