Unbelievable.

Unbelievable, incredible.

Not credible: that cannot be believed; beyond belief.

Unbelievable, incredible. Obsolete.

Not opinable; unthinkable, inconceivable; not to be thought of.

That cannot be believed; incredible.

Unworthy of belief, not credible. rare.

too good to be true: expressing disbelief or doubt that something could genuinely be as good as it seems.

In weaker or more general sense: That cannot be understood; inconceivable, unintelligible.

Not to be believed; = incredible, adj. Obsolete.

Disqualified from being a witness or giving evidence.

That cannot be conceived or realized in the imagination; unthinkable, unimaginable, incredible. Often with exaggerative force for ‘hardly credible’…

Not persuasive, unconvincing; lacking the power to persuade.

= inconceivable, adj.