Dictionary

oath

a promise that that a person will tell the truth (especially in a court of law), especially one that makes reference to God or to a holy book I must remind you that you are under oath. Think very carefully before answering the question.

Phrase Bank

  • She swore on oath that it was not true.
  • The witness refused to testify (=give evidence in court) under oath.
  • It is time for the new president to take the oath of office.

Additional Notes

  • Under oath is used in AmE and BrE, whereas on oath is only a BrE usage.