baseless
adj.not based on any facts or evidence. You use this to describe a claim or an idea that is completely untrue and has no proof.
adj.lacking a foundation in fact or evidence; groundless. Often used to describe accusations, rumors, or fears that have no empirical support.
“The company dismissed the rumors as completely baseless.”
“The politician claimed the allegations were baseless and intended only to damage his reputation during the election.”
“Legal experts argued that the lawsuit was entirely baseless, as the plaintiff failed to provide a single piece of evidence to support the claim of negligence.”
Typically used attributively before a noun or predicatively after a linking verb like 'be' or 'remain'.
“In addition, several candidates who lost their race for local office have embraced baseless conspiracy theories about election fraud and sued to overturn results.”
From base + -less.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.