The part of the speech is : Adverb.
Explanation:
An adverb is a word or an expression that is used in English Grammar that modifies a verb, an adjective, a determiner, a clause, a sentence or a preposition also.
It adds a quality to all these expressing their relation with time, place, circumstance, cause, degree or the manner. They are intensifiers and they even come in the form of an adverb phrase.
