Just as nouns can function like adjectives, as we highlighted in our previous post, so can adjectives function like nouns.
Merriam-Webster editor Neil Serven gives us an explanation:
For example, the words poor and sick are easily recognizable as adjectives:
We were too poor to afford a car.
He was sick with a head cold.
As with most adjectives, poor and sick can be used before a noun to modify that noun:
a sick patient
But what happens when such an adjective is preceded by the but not followed by a noun?
She gives money to the poor.
Nurses care for the sick.
The words poor and sick here are used to refer to poor people and sick people, respectively, with the nouns they modify omitted. While they function like nouns here, they are not defined as nouns because they do not meet any of the other criteria that typically distinguishes a word as a noun.
A lot of adjectives are used this way, many referring to classes of people:
a shelter for the homeless
a word to the wise
the meek shall inherit the earth
tax breaks for the insured
A lot of these kinds of adjectives can be found in titles of works. The title of Norman Mailer’s novel The Naked and the Dead contains two adjectives that are essentially functioning as nouns. The same goes for Stendhal’s The Red and the Black and F. Scott Fitzgerald’s The Beautiful and Damned. Consider also the Martin Scorsese film The Departed or the American TV soap opera The Young and the Restless.