oath

1. A solemn pledge or promise, appealing to a deity, a ruler, or another entity (not necessarily present) to attest to the truth of a statement or sincerity of one's desire to fulfill a contract or promise.
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.

3. A light, irreverent or insulting appeal to a deity or other entity.
4. A curse, a curse word.

verb

To pledge.