Difference Between Oaf and oathOaf means an insult indicating someone who is regarded as unintelligent, clumsy, or uncultured: “Oh, stop knocking things over, you oaf!”

Oath , on the other hand, means the following:-
1. A solemn, formal declaration or promise to fulfill a pledge, often calling on God, a god, or a sacred object as witness: “The oath taking ceremony of Barrack Obama, first black president of the US, was covered by media all over the world.”
2. A formal and serious promise to tell the truth or to do something: “The witnesses are required to take an oath of Bhagvad Gita in the courts before giving a testimony.”
3. An irreverent or blasphemous use of the name of God or something held sacred: “She expressed her anger towards the corrupt administrator by uttering an oath.”