An adjectival phrase is a group of words that modify or describe a noun or pronoun in a sentence. There are a handful of different terms that can be used interchangeably with adjectival phrase, including adjective phrase, adjective clause, and relative clause. An adjective phrase, by definition, is a group of words that serves as an adjective in a sentence, typically by describing a noun. An adjective clause, on the other hand, is a dependent clause that functions as an adjective, often beginning with relative pronouns like who and which. Finally, a relative clause is similar to an adjective clause, but it can also be used to provide additional information about a subject or object of a sentence.