Without fault or weakness; incapable of error or fallacy.
Certain to produce the intended effect, sure.
A person who, or an object or process that, is taken as being infallible.
Physically secure and certain, non-failing, reliable.
Certain to act or be a specified way.
Certain in one's knowledge or belief.
Yes, expressing noncommittal agreement or consent.
Yes; of course.
You're welcome; polite response to being thanked.
Without doubt, certainly.