Green’s Dictionary of Slang

rapper n.2

[rap v.1 ]

1. [late 18C–1900s] a professional perjurer.

2. [1900s–60s] (US) a plaintiff, a prosecutor.

3. [1920s–30s] (US Und.) an informer.

4. [1920s–40s] (US Und.) a judge.

5. [1940s] (US) one who takes or is given the blame for a crime, even if they are not actually guilty.

6. [1960s+] (US) a chatterer, a talker.

7. [1960s+] (US) the voice.

8. [1970s+] (US black) one who talks articulately and persuasively.