An adjectival noun refers to an adjective that functions as a noun.

In inflected languages like German, adjectival nouns are much more common however.

Old Japanese has one type of adjectival noun with the following inflections.

Late Middle Japanese has two types of adjectival nouns: na and t-.

There is one type of adjectival noun in modern usage, with inflections as follows.

There were two types of adjectives: regular adjectives and adjectival nouns.

Historically the adjectival noun was sub-classified into two categories: -nar and -tar.

Japanese adjectival nouns are a different concept.

Then there are occasions when an apostrophe is not needed - for adjectival nouns.

This choice has some support in Japanese scholarship, though traditionally these words are referred to as "na-adjectives" or "adjectival nouns".