An adverb is simply a word that describes a verb (an action or a doing word). The word quickly is an adverb as it tells us how he ate (the verb) his breakfast.
A word that describes or gives more information about a verb, adjective, adverb, or phrase 2.
An adverb refers to any element in a sentence used to modify a verb, adjective, another adverb, or even an entire clause.
ADVERB | meaning in the Cambridge English Dictionary
An adverb is a word or an expression that modifies a verb, adjective, another adverb, determiner, clause, preposition, or sentence. Adverbs typically express manner, place, time, frequency, degree, level of certainty, etc. , answering questions such as how?, in what way?, when?, where?, and to what extent. This is called the adverbial function, and may be performed by single words (adverbs) or by multi-word adverbial phrases and adverbial clauses.
An adverb is a part of speech that provides greater description to a verb, adjective, another adverb, a phrase, a clause, or a sentence.