1.NounA 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"
2.NounA 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."
3.NounA light, irreverent or insulting appeal to a deity or other entity.