Answer:
Adverb.
Step-by-step explanation:
An adverb can be defined as a word that is used in English language to modify a verb, adjective, or another adverb. Some examples are slowly, quickly, brightly, sadly, etc.
Generally, adverbs are formed by adding the suffix "ly" to the end of a verb e.g mistake + ly = mistakenly.
Hence, an adverb is one of the parts of speech in English language and it refers to a word that modifies (describes) a verb, an adjective another adverb, or even a whole sentence. Also, some adverb such as fast are exactly the same as their adjective counterparts​. For example, she is fast asleep, my wrist-watch is running fast, do it as fast as you can, etc.