take an oath

WordReference Random House Learner's Dictionary of American English © 2025

oath /oʊθ/   n. [countable] , pl. oaths (ōᵺz, ōths).

1. a solemn declaration to God, a god, or some person or thing that is sacred, that what one says is the truth, or that what one promises will be done.
2. an irreverent use of the name of God or of anything sacred.
3. a curse word.

Idioms

4. Idioms take an oath, to swear solemnly;
   vow:
   He took an oath to care for his niece.
   [~ + that clause]
   He took an oath that he would care for his niece.
5. Idioms under oath, [uncountable] solemnly bound by the obligations of an oath.

WordReference Random House Unabridged Dictionary of American English © 2025

oath  (ōth), n., pl. oaths  (ōᵺz, ōths). 

1. a solemn appeal to a deity, or to some revered person or thing, to witness one's determination to speak the truth, to keep a promise, etc.:
   to testify upon oath.
2. a statement or promise strengthened by such an appeal.
3. a formally affirmed statement or promise accepted as an equivalent of an appeal to a deity or to a revered person or thing;
   affirmation.
4. the form of words in which such a statement or promise is made.
5. an irreverent or blasphemous use of the name of God or anything sacred.
6. any profane expression;
   curse;
   swearword:
   He slammed the door with a muttered oath.
7. take an oath, to swear solemnly;
   vow.

• bef. 900; Middle English ooth, Old English āth; cognate with German Eid

Synonyms

• 2. vow, pledge.
• 5. profanity.

Collins Concise English Dictionary © HarperCollins Publishers::

oath / əʊθ/ noun ( oaths / əʊðz/)

1. a solemn pronouncement to affirm the truth of a statement or to pledge a person to some course of action, often involving a sacred being or object as witness
2. the form of such a pronouncement
3. an irreverent or blasphemous expression, esp one involving the name of a deity; curse
4. on oath, upon oath, under oath ⇒ under the obligation of an oath
5. having sworn to tell the truth, usually with one's hand on the Bible
6. take an oath ⇒ to declare formally with an oath or pledge, esp before giving evidence

Etymology: Old English āth; related to Old Saxon, Old Frisian ēth, Old High German eid