OATH

noun (plural ~s) Etymology: Middle English ooth, from Old English āth; akin to Old High German eid ~, Middle Irish oeth Date: before 12th century 1. a. a solemn usually formal calling upon God or a god to witness to the truth of what one says or to witness that one sincerely intends to do what one says, a solemn attestation of the truth or inviolability of one's words, something (as a promise) corroborated by an ~, an irreverent or careless use of a sacred name