To swear, to make a binding statement about s.t. (as of an oath of enmity or friendship).
Often s.t. that is impossible to happen is mentioned as the condition for doing s.t. E.g., if my grandfather rises from the dead only then will I do such and such; or, only when my foot is cut off will I come, etc. If s.o. has sworn like that, he needs to have a prayer ceremony in order to be forgiven.
She swears that she will not go back to her husband.
Magsubali siye magpungtina'ihin.
The siblings swear to each other.
Those people often swear.
She swore to me that she would only come to my house when her grandmother rises from her grave.