Ignore the last sentence in >>424, disconnect between what I meant and what I typed.
Adding -er only works with certain things and it does somtimes work with nouns.
It is mostly used with verbs to make nouns (one that does verb), but it can be used with nouns in some cases(mostly in denoting citizenship such as New York (place) -> New Yorker (one that lives in New York or is characteristic of New York) but even then it isn't uniform (There is also -ian which is used in some cases Boston (place) -> Bostonian (one that lives in Boston or is characteristic of Boston)).