ill-founded

Adjective

ill-founded (comparative more ill-founded, superlative most ill-founded)

1. Unsubstantiated, not based on fact or evidence.
   • ill-founded criticism
   • He said, the part of the sentence which stated that the court “having heard the evidence, and maturely and seriously considered the whole, are of opinion that the charge is malicious and ill-founded: […]”1814, Cobbett's Parliamentary History of England: From the Norman Conquest, in 1066 to the Year 1803., page 1155

   Synonyms:

   ill-grounded, groundless, baseless, flimsy, unjustified

   Antonyms:

   well-grounded, well-founded, on solid ground