grammar - Verb and adjective usage

Since adjectives are used to describe nouns, can verbs be used to describe nouns as well?

For example:

Two men standing with clenched fists are US athletes.

Here fist is a noun and to describe a noun, an adjective is used. In this case the adjective should be clenched but the dictionary shows that clenched is a verb.

So does that mean that verbs are also used to describe nouns?