Is miss an abbreviation for missus?

Answer 1

No, it is not. Miss refers to an unmarried woman, and missus is the long form of "mrs.", which refers to a married woman. Both derive from "mistress", but refer to a different marital status. Ms. (pronounced "miz") refers to any woman, and does not reflect her marital status. It is particularly appropriate when a woman's marital status is unknown or she is older and unmarried for any reason.