Too implausible to be credible; beyond belief; unbelievable.
Amazing; astonishing; awe-inspiring.
Marvellous; profoundly affecting; wonderful.
(of an adjective) Describing a quality that cannot normally be varied because it is extreme (e.g. freezing), absolute (e.g. dead), or classification (e.g. nuclear).
That cannot be graded.
Any adjective that is not gradable.