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Related to under oath: swear under oath
Bound by a formal promise to tell the complete and honest truth about an event while on the witness stand in a trial. You are under oath as a witness in this trial, so you must answer my questions completely truthfully! Consider your answer carefully—you're still under oath.
Fig. bound by an oath; having taken an oath. You must tell the truth because you are under oath. I was placed under oath before I could testify in the trial.
on/under ˈoath(law) having made a formal promise to tell the truth in a court of law: Is she prepared to give evidence on oath? ♢ The judge reminded the witness that he was still under oath.
Under a burden or responsibility to speak truthfully or perform an action faithfully.