Under oath is a legal term that refers to a person's obligation to tell the truth while giving testimony. Synonyms for this phrase include "sworn in," "sworn statement," "affirmation," or "declaration." When someone is under oath, they are legally bound to provide truthful information or risk facing perjury charges. Other variations of these terms include "oath-taking," "swearing under penalty of law," and "taking an oath of truthfulness." Regardless of the phrasing used, being under oath is a serious matter that requires an individual to provide honest and accurate testimony, and therefore, should not be taken lightly.