The term ‘American’ is considered a proper noun when it refers specifically to a person from the United States or something related to the country. For example, in the sentence, ‘She is an American,’ the word ‘American’ is a proper noun because it denotes a specific nationality.
On the other hand, ‘American’ can also function as a common noun in certain contexts, particularly when describing a general characteristic or aspect of American culture, such as in ‘Many Americans enjoy football.’ In this case, it refers more broadly to the group of people rather than a specific identity.
In summary, whether ‘American’ is a common or proper noun depends on its usage in the sentence. Most often, it serves as a proper noun when identifying nationality.