A nominalized adjective is an adjective that has undergone nominalization, and is thus used as a noun. In the rich and the poor, the adjectives rich and poor function as nouns denoting people who are rich and poor respectively.

The most common appearance of the nominalized adjective in English is when an adjective is used to indicate a collective group. This happens in the case where a phrase such as the poor people becomes the poor. The adjective poor is nominalized, and the noun people disappears. Other adjectives commonly used in this way include rich, wealthy, homeless, disabled, blind, deaf, etc., as well as certain demonyms such as English, Welsh, Irish, French, Dutch.

Another case is when an adjective is used to denote a single object with the property, as in "you take the long route, and I'll take the short". Here the short stands for "the short route". A much more common alternative in the modern language is the structure using the prop-word one: "the short one". However, the use of the adjective alone is fairly common in the case of superlatives such as biggest, ordinal numbers such as first, second, etc., and other related words such as next and last.

Many adjectives, though, have undergone conversion so that they can be used regularly as countable nouns; examples include Catholic, Protestant, red (with various meanings), green, etc.

Nominal uses of adjectives have been found to have become less common as the language developed from Old English to Middle English and then Modern English. The following table shows the frequency of such uses in different stages of the language:

The decline in the use of adjectives as nouns may be attributed to the loss of adjectival inflection throughout Middle English. In line with the Minimalist Framework elaborated by Noam Chomsky, it is suggested that inflected adjectives are more likely to be nominalized because they have overtly-marked φ-features (such as grammatical number and gender), which makes them suitable for use as the complement of a determiner.

Determiners with unvalued φ-features must find a complement with a valued φ-feature to meet semantic comprehension. In the diagrams below, the determiner is the, and its complement is either the noun phrase poor people or the nominalized adjective poor.

The capacity of adjectives to be used as nouns is sometimes exploited in puns like The poor rich.