Is August a common or proper noun?

August is a proper noun. It can be the name of a person or the name of a month.

Nouns refer to people, places, and things. Nouns can be divided into proper nouns and common nouns. Proper nouns are names for specific people, places, events, and things, such as Christopher Columbus, Santa Maria, and North America, and are capitalized. Common nouns are nouns that refer to types of people, places, and things, such as sailor, ship, continent, salmon, and victory, and are not capitalized except at the beginning of a sentence. August is a proper noun because it refers to a specific person or a specific month.