Undeniable means impossible to dispute or argue against because it's so obviously true. When something is undeniable, the evidence is so strong that even people who might want to disagree can't reasonably do so.

If you score the winning goal in a soccer championship, your contribution to the victory is undeniable. When a student consistently earns perfect scores on every math test, their understanding of the material is undeniable. The word suggests that the facts speak for themselves so clearly that denial would be absurd or dishonest.

You might hear someone say “It's undeniable that practice improves performance” or “The fossil evidence for dinosaurs is undeniable.” These statements mean the truth is so well-established that arguing against it makes no sense.

An undeniable fact is one that stands up to scrutiny or challenge. An undeniable truth remains true no matter how much someone might wish otherwise.