The word ‘American’ can function as both a noun and an adjective, depending on the context in which it is used.
As a noun, ‘American’ refers to a person from the United States or someone who is a citizen of America. For example, in the sentence, ‘She is an American.’, ‘American’ identifies the nationality of the subject.
As an adjective, ‘American’ describes something that is related to or characteristic of the United States. For instance, in the sentence, ‘He loves American music.’, ‘American’ describes the type of music being referred to.
In summary, ‘American’ can be a noun or an adjective based on its usage in a sentence.