Why is derby kelly rhyming slang for belly?

"Derby Kelly" is rhyming slang for "belly" because it rhymes with "belly." This is a classic example of how rhyming slang works.

Here's how it breaks down:

* Rhyming Slang: A form of slang where a phrase is used to replace a word, with the phrase chosen because it rhymes with the word being replaced.

* "Derby Kelly" rhymes with "belly."

* The meaning: "Derby Kelly" is used as a slang term for "belly."

It's important to note that rhyming slang can be very regional and can change over time. While "Derby Kelly" might be a common term in some parts of the UK, it might not be recognized elsewhere.