superlative vs nighest

superlative is a noun but nighest is not a noun.

Word	Noun	Adjective	Verb	Adverb
superlative	Yes	Yes	No	No
nighest	No	No	No	Yes

superlative (noun)	nighest (noun)
an exaggerated expression (usually of praise)
the superlative form of an adjective or adverb
the highest level or degree attainable; the highest stage of development

superlative (adjective)	nighest (adjective)
highest in quality

superlative (adverb)	nighest (adverb)
	(superlative of `near' or `close') within the shortest distance