on/under oath

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.
See also: oath

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.
See also: oath, on

under oath

Under a burden or responsibility to speak truthfully or perform an action faithfully.
See also: oath