In English grammar, what part of speech is 'quickly'?

In English grammar, “quickly” is an adverb.

An adverb is a word that commonly modifies a verb, adjective, another adverb, or an entire clause. In “She ran quickly,” the word explains how she ran, modifying the verb “ran.” It answers a question such as how, when, where, or to what extent.

“Quickly” is formed from the adjective “quick” with the productive suffix “-ly,” a common pattern in English: slowly, carefully, brightly, and fortunately work similarly. The adjective “quick” describes a noun, as in “a quick response,” while “quickly” describes an action or manner, as in “responded quickly.”

The category is useful but not always identified by spelling alone. Some adverbs do not end in “-ly,” including very, often, soon, here, and fast. Conversely, some “-ly” words, such as friendly and lovely, are usually adjectives rather than adverbs. In “quickly finished,” the adverb modifies “finished,” not a noun.