The word "adverb" is a noun. An adverb, a word that modifies a verb, adjective, or adverb, is its 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.