Is the word "adjectival" used in this context?

Yes, "adjectival" is used in context. Yes, "adjective clause" is also commonly used as English can also make nouns act like adjectives. They can become modifiers, called noun adjuncts.

adjectival clause or relative clause or adjective clause

An adjectival clause (or relative clause) is one that modifies a noun phrase. They typically are introduced by a relative pronoun, which serves as the subject of the clause. For example: The man who lived here went to New York. The car that came from Italy is very fast. The apple which fell from my bag is now inedible.

adjectival clause

there are adverbial clauses, and for parallelism's sake, there are adjectival clauses AKA relative clauses.

Relative clause In Indo-European languages, a relative clause, also called an adjectival clause or an adjective clause, meets three requirements:

adjectival

Sometimes, things are known by several different names.