Theologically, a mental reservation ( no it is not a nut-house for Indians)- in Law, lying under oath- in the course of a trial or or similar proceedings is called Perjury- and is a punishable offense. Do not confuse with that long-suffering 5TH AMENDMENT.
Of course. Being under oath does not make you infallible.
If you're inquiring as to what "oath" means in terms of speaking "under oath," then the following (from wikipedia) is likely an adequate answer: An oath (from Anglo-Saxon āð) is either a promise or a statement of fact calling upon something or someone that the oath maker considers sacred, usually a god, as a witness to the binding nature of the promise or the truth of the statement of fact. To swear is to take an oath. Or simply stated, it is a promise to tell the truth.
Promise to swear allegiance to the U.S. and to follow its laws and the Constitution.
A solemn promise is often referred to as an oath. It is a formal declaration or promise typically made with a strong sense of responsibility or commitment.
While taking Oath as newly inducted citizens of USA, one has to promise to bear arms in defense of the country if time comes. This promise is unique to USA oath.
perjury
promise
pledge, promise, swear
promise
pledge
what is another word for promise? A vow or an oath