Adjective in the sentence: old

Explanation:
An adjective is a word that describes or modifies a noun or pronoun. It provides additional information about the noun or pronoun in terms of its quality, size, shape, color, etc.

In the given sentence, "The old man walked slowly across the street," the adjective is "old." It describes the noun "man" and gives us information about the age of the man. The word "old" adds descriptive detail to the sentence by telling us that the man is not young.

Here's a breakdown of the sentence:

- The (article) is a definite article that introduces the noun and indicates that it is a specific man being referred to.
- old (adjective) describes the noun "man" and provides information about his age. It gives us a sense of the man's maturity or experience.
- man (noun) is the subject of the sentence, referring to an adult male human.
- walked (verb) is the action performed by the man. It tells us what the man did.
- slowly (adverb) describes the manner in which the man walked. It provides information about the speed or pace of his walking.
- across (preposition) indicates the direction or location of the street the man walked.
- the (article) is a definite article that introduces the noun "street" and indicates that it is a specific street being referred to.
- street (noun) is the object of the verb "walked." It refers to a public road in a town or city.

Therefore, in the given sentence, the adjective is "old" as it modifies the noun "man" and provides additional information about his age.