What part of speech is only in Americans?

This is a bit of a trick question! There's no part of speech that exists *only* in American English. All the traditional parts of speech (nouns, verbs, adjectives, adverbs, etc.) are found in both American and British English, and many other varieties of English as well.

However, there are some differences in how words are used in American vs. British English, such as:

* Vocabulary: Some words have different meanings or are used differently (e.g., "fall" vs. "autumn").

* Grammar: There are some slight differences in grammar, like the use of "gotten" vs. "got."

* Pronunciation: Some words are pronounced differently (e.g., "tomato").

So, while there's no unique part of speech, there are interesting variations in how English is used across different dialects.