Indubitable means impossible to doubt or question. When something is indubitable, it's so clearly true that no reasonable person could disagree with it.

If you solve a math problem and check your work three different ways, all giving the same answer, that answer is indubitable. When a detective finds fingerprints, video footage, and eyewitness accounts all pointing to the same person, the evidence becomes indubitable.

You might say “It's an indubitable fact that water freezes at 32 degrees Fahrenheit” or “The team's victory was indubitable after they scored their fifth goal.” Scientists often search for indubitable proof before announcing a discovery, wanting evidence so strong that other scientists can't reasonably question it.

Indubitable is a formal word that adds weight to what you're saying. It's stronger than just saying something is “obvious” or “clear.” When you call something indubitable, you're saying the evidence or logic is so overwhelming that doubt would be unreasonable. The related adverb indubitably means “without a doubt” and sounds particularly confident and proper, like something a Victorian detective might say while solving a mystery.