non-gradable vs uncomparable

non-gradable

• That cannot be graded. 

• (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). 

• Any adjective that is not gradable. 

uncomparable

• Not able to be compared; not comparable. 

• Not comparable.