The word "subside" typically refers to a decrease or calming of intensity, as in a storm subsiding. Its antonyms, or opposites, would therefore be words that describe an increase in intensity. Some examples might include "escalate," "intensify," "surge," "flourish," or "proliferate." Other antonyms for subside could describe a lack of calm or decrease, such as "agitate," "fluctuate," "worsen," or "exacerbate." Depending on the context in which the word is used, there may be a variety of appropriate antonyms to choose from.