1. noun
a) A solemn pledge or promise to a god, king, or another person, to attest to the truth of a statement or contract
for they made Ocean and Tethys the parents of creation, and described the oath of the gods as being by water,
b) the affirmed statement or promise accepted as equivalent to an oath
2. verb
a) (archaic) To pledge.
b) Shouting out. (as in oathing obsenities)
Wikipedia foundation.