Which type of subordinate clause modifies a noun?

An adjective clause (also called a relative clause), just like an adjective, modifies the noun or pronoun preceding it (also called the antecedent).

Adjective Clause

The type of subordinate clause that modifies a noun is called an adjective clause. As you may know, a word that modifies a noun is called an adjective. The same rule/naming convention applies to clauses: If a clause modifies a noun, it is called an adjective clause. For instance in the following sentence, the adjective is in bold:

The big tree fell.

Thus, because the noun "tree" is modified by the word "big," the adjective is "big." Now, let’s use a subordinate clause to modify "tree":

The tree, which was big, fell.

Here, you can see that an entire clause is modifying the noun; thus, the entire clause is serving as an adjective and is therefore termed an adjective clause.