oath

Etymology

From Middle English ooth, oth, ath, from Old English āþ (“oath”), from Proto-West Germanic *aiþ (“oath”), from Proto-Germanic *aiþaz (“oath”), from Proto-Indo-European *h₁óytos (“oath”). Cognate with Scots aith, athe (“oath”), North Frisian ith, iss (“oath”), West Frisian eed (“oath”), Dutch eed (“oath”), German Eid (“oath”), Swedish ed (“oath”), Icelandic eið (“oath”), Latin ūtor (“use, employ, avail”), Old Irish óeth (“oath”).

noun

1. A solemn pledge or promise that invokes a deity, a ruler, or another entity (not necessarily present) to attest the truth of a statement or sincerity of one's desire to fulfill a contract or promise.
   take an oath
   swear an oath
   break one's oath
   But all of us took an oath to do our duty when we joined the Space Force, and I fully expect everyone to willingly keep their word. But you took no oath, and have no obligation. 2007, George Simmons Roth, Battle in Outer Space
   There are […] brought all the way from Bougainville to present their birth certificates and testify in this courtroom, under oath, as to their given names. 2011, Mark Leyne, The Tetherballs of Bougainville: A Novel
2. A statement or promise which is strengthened (affirmed) by such a pledge.
   After taking the oath of office, she became the country's forty-third premier.
   The generals swore an oath of loyalty to the country.
   Wrex: [sigh] Before I left, I made an oath to my father's father. Wrex: I swore to recover my family's battle armor. It was taken from him after the uprising. 2008, BioWare, Mass Effect (Science Fiction), Redwood City: Electronic Arts, →OCLC, PC, scene: Normandy SR-1
3. A light, irreverent or insulting appeal to a deity or other entity.
4. A curse, a curse word.
   The farther from the Senator's office, the darker and older the furniture, the freer fly four-letter oaths, the higher the heaps of unfiled and unattended papers culminating in a frenzy of pulp in the press section[…] 1981, Bernard Asbell, The Senate Nobody Knows

verb

1. (archaic) To pledge.