The word adverb is a noun. However, adverbs (the words that modify verbs, adjectives, and other adverbs) are their own part of speech.
adverb
adverb
Adverb
Adverb
"Ever" is an adverb.
Supposedly is an adverb.
Steadily is an adverb.
adverb
Commonly is an adverb.
Twice is an adverb.
Beautifully is an adverb.
Hysterically is an adverb.