groundless
Not having any real reason, proof, or support.
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.