"Sit it out" can be defined as intentionally avoiding participation in a situation or event. This phrase can have various synonyms depending on the context. Some of the most common synonyms include "stay on the sidelines," "watch from the sidelines," "opt-out," "decline," "abstain," "refrain," "withdraw," "stay away," and "take a back seat." Each of these phrases has a slightly different connotation and should be chosen based on the specific situation. For instance, "opt-out" and "decline" are often used when declining an invitation or request while "stay away" and "take a back seat" are more commonly used when avoiding involvement in a larger issue.