When it comes to antonyms for the word "relaxation," there are several terms that come to mind. One such term is "tension," which refers to a state of mental or emotional strain. Another antonym could be "stress," which describes the feeling of being overwhelmed or anxious. "Anxiety" is another antonym that describes a sense of unease or worry. Additionally, "pressure" could be used as an antonym for relaxation, which means the feeling of being pushed or stressed to perform. Finally, "work" is another antonym as it implies effort and mental or physical labor rather than rest and leisure.