Forbidding describes something that looks unwelcoming, threatening, or difficult to approach. A forbidding castle might have high stone walls, narrow windows, and an overall appearance that makes you think twice about knocking on the door. A forbidding mountain range could be covered in jagged peaks and dark clouds that make climbers nervous. Even a person can have a forbidding expression: stern, cold, and unapproachable, like a principal who looks so serious that students hesitate to ask questions.

The word captures that feeling when something makes you want to stay away, not because of any specific danger but because of its atmosphere. A forbidding forest might be perfectly safe, but its dense shadows and tangled undergrowth create an uninviting mood. A forbidding building might simply look severe and unfriendly rather than actually dangerous.

A forbidding place or person seems to forbid your approach just by appearance, even without saying a word. It's the visual equivalent of a “Keep Out” sign: everything about it suggests you're not welcome, whether that's actually true or not.