Definition from Nolo’s Plain-English Law Dictionary
1) To declare under oath that one will tell the truth (sometimes "the truth, the whole truth, and nothing but the truth"). Failure to tell the truth, and to do so knowingly, is the crime of perjury. 2) To administer an oath to a witness that he or she will tell the truth, which is done by a notary public, a court clerk, a court reporter, or anyone authorized by law to administer oaths. 3) To install into office by administering an oath.