Groundless means lacking any basis in fact or evidence. When an accusation is groundless, there's no proof or reason to support it. When a fear is groundless, nothing real justifies the worry.

A groundless rumor spreads without any actual information behind it. Groundless suspicions exist only in someone's imagination, not in reality.

You might hear that someone's concerns were groundless after a situation turns out fine. If you worried all week about failing a test you actually passed easily, those worries were groundless. If a friend accuses you of something without any evidence, that's a groundless accusation.

The word often appears when someone realizes their beliefs or fears had no foundation. A detective might discover that groundless speculation wasted everyone's time, or a scientist might prove that an old theory was groundless. When something turns out to be groundless, it means the whole thing was built on nothing, like a castle in the clouds that looks real from a distance but vanishes when you get close.