Q From Anthony Pennock: Why do we say no soap?
A The word soap has had several slang meanings down the years. In the middle nineteenth century in the USA it was used to mean money, though we don’t know why. It’s first recorded about 1860, but by then was probably well established. So somebody who said “No soap!” meant something like “No, I haven’t any money” or “No, I won’t give you a loan”. The modern sense — nothing doing, not a hope, no chance — is a generalisation. Americans have kept no soap but have forgotten the sense of soap that it sprang from.