Undeniable means something that cannot be doubted or questioned. It is something that is certain and without a doubt. For example, if someone says "The sun rises in the east," this statement is undeniable because it's an indisputable fact. Another example would be if someone said "I have never lied to you," this too could be considered undeniable because there's no way to disprove it since you can't know for sure what someone else has done in the past.