unequivocal
Completely clear and leaving no room for doubt.
Unequivocal means completely clear, with no room for doubt or different interpretations. When something is unequivocal, there's no confusion about what it means.
If your teacher gives you unequivocal instructions to turn in your project by Friday, she means Friday, no exceptions, no wiggle room. If a referee makes an unequivocal call that the ball went out of bounds, there's no question about it: everyone saw it clearly cross the line.
When a witness gives unequivocal testimony in court, their statement is straightforward and consistent. When scientists find unequivocal evidence for something, the data points in only one direction.
You might hear someone say they unequivocally support a decision, meaning they support it completely, without reservation. Or a friend might give you an unequivocal “no” when you ask to borrow something precious, making it crystal clear the answer isn't changing. Unequivocal statements leave no room for misunderstanding.