No, the word 'guilty' is not a noun, it is an adjective(guilty, guiltier, guiltiest), a word used to describe a noun.
A noun is a word for a person, a place, or a thing.
A pronoun is a word that takes the place of a noun in a sentence.
Examples:
The guilty prisoner was sentenced to life. He was then led from the courtroom.
- the adjective 'guilty' describes the noun 'prisoner', a word for a person;
- The pronoun 'he' takes the place of the noun 'prisoner' in the second sentence.