According to Merriam-Webster Dictionary, the word pretty is an adjective, but it can also be an adverb, a noun, and a verb. — I guess you’re pretty much confused now. 😀
Pretty is an aderb; meaning quite, very, somewhat
• He’s a pretty good student.
• How are you — Pretty good.
• How does she look? — Pretty nice.
• The wind blew pretty hard.
Pretty much is an idiom; meaning for the most part; mostly.
• The village was pretty much destroyed after the earthquake.
• The matter was pretty much dying down.