1
general::
A prostitute, an immoral woman, as in Malicious gossip had it that she was a scarlet woman, which was quite untrue. This expression first appeared in Revelation 17:5, describing Saint John's vision of a woman in scarlet clothes with an inscription on her forehead, "Mystery, Babylon the Great, the mother of harlots and abominations of the earth." Some interpreters believe she stood for Rome, drunk with the blood of saints, but by about 1700 the term was being used more generally for a woman with loose morals.
American Heritage Idioms