un ‧ found ‧ ed AC /ʌnˈfaʊndəd, ʌnˈfaʊndɪd/ BrE AmE adjective
unfounded statements, feelings, opinions etc are wrong because they are not based on facts
unfounded rumours/claims/allegations etc
Unfounded rumours began circulating that Ian and Susan were having an affair.
prove (to be) unfounded
Sadly, my optimism proved unfounded.