What type of word expresses action or links the subject to a description?

The term that expresses action or links the subject to a description is a verb. Verbs are essential components of sentences because they denote what the subject is doing or state what the subject is like. In the case of action verbs, they explicitly describe an activity (e.g., "run," "jump," "think"), while linking verbs connect the subject to additional information, often through adjectives or predicate nouns (e.g., "is," "seem," "become").

This function of linking or expressing action differentiates verbs from other parts of speech. Nouns primarily serve as names of people, places, things, or ideas and do not convey action or descriptions in the same way. Adjectives describe nouns and provide information about qualities or characteristics but do not express actions. Adverbs modify verbs, adjectives, or other adverbs, often describing how, when, where, or to what extent an action is performed, but they also do not express an action by themselves. Therefore, the role of a verb is unique and critical to constructing meaningful sentences.