without a basis in reason or fact; "baseless gossip"; "the allegations proved groundless"; "idle fears"; "unfounded suspicions"; "unwarranted jealousy"
If you describe a rumour, belief, or feeling as unfounded, you mean that it is wrong and is not based on facts or evidence. There were unfounded rumours of alcohol abuse The allegations were totally unfounded = groundless. unfounded statements, feelings, opinions etc are wrong because they are not based on facts unfounded rumours/claims/allegations etc