na-adjective, noun
baseless; groundless; unfounded
Used for claims, accusations, or beliefs that lack any factual basis or evidence. Often appears in formal or argumentative contexts.
その批判はまったく無根拠だ。
That criticism is completely unfounded.
無根拠な噂を広めるべきではない。
You shouldn't spread baseless rumors.
事実無根 is a set phrase meaning 'completely untrue' or 'groundless', often used in legal or formal denials.
Compound of 無 (mu, 'without') and 根拠 (konkyo, 'basis, grounds'). The reading むこんきょ follows standard on'yomi.