1) Baseless 2) Groundless 3) Idle 4) Inexcusable 5) Not established 6) Type of rumor 7) Unfair 8) Unjustifiable 9) Unjustified 10) Unpardonable 11) Unsubstantiated 12) Unsupported 13) Unwarranted 14) Without foundation Found on https://www.crosswordclues.com/clue/unfounded
without foundation; not based on fact, realistic considerations, or the like: unfounded suspicions. · not established; not founded: the prophet of a religion as yet unfounded. Found on https://www.infoplease.com/dictionary/unfounded