oath

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

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.

A light, irreverent or insulting appeal to a deity or other entity.

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[…]

To pledge.