What is the term for a form of the verb used as an adjective?

The term for a form of the verb used as an adjective is participle. Participles can be categorized into two types: present participles, which typically end in -ing (e.g., "running," "swimming"), and past participles, which usually end in -ed, -en, or other irregular forms (e.g., "washed," "broken").

Participles function to modify nouns, thereby providing more information about the subject. For example, in the phrase “the running water,” the present participle “running” describes the noun “water.” The use of participles allows for more descriptive and nuanced writing by connecting actions directly to the nouns they describe.

Other options such as noun, verb, and adverb do not serve the same purpose. Nouns represent people, places, or things; verbs indicate actions or states; and adverbs modify verbs, adjectives, or other adverbs rather than nouns. Therefore, participles specifically fulfill the role of an adjective, making them the correct answer in this context.