Certainty (noun)

1. The state of being certain; the quality of being sure or certain.
2. A fact or truth that is known or certain.

Origin:

From old french certeine, from latin certus ("fixed, settled, sure, certai.n")

Examples:

1. She spoke with certainty about the outcome of the election.
2. The scientist expressed certainty that the new theory was correct.
3. The outcome of the game was a certainty.
4. The certainty of death and taxes is a famous quote from Benjamin Franklin.
5. There is no certainty in life, only probability.