Fairly is an adverb.
The word "fairly" can be used as an adverb, modifying adjectives or other adverbs to indicate degree or extent.
I'm fairly sure it's an adjective but look it up in a dictionary to be certain.
Verb
After the speech, all black people were treated fairly.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.
The part of speech for "rapid" is an adjective.