"Ex action" refers to an activity or behavior that was previously taken by someone. The antonyms for this word can vary depending on the context of the sentence, but some possible opposites include inaction, cessation, and nonperformance. Inaction refers to the absence of any action or behavior, while cessation denotes the act of stopping or halting an activity. Nonperformance, on the other hand, suggests a failure to carry out a task or action. Finding the appropriate antonym for "ex action" depends on the specific situation and the desired meaning of the sentence.