Green’s Dictionary of Slang

door-knocker n.

[supposed similarities]

1. [mid–late 19C] a beard that runs along and just beneath the jaw line; when linking up with a moustache it was seen as resembling a door-knocker.

2. [late 19C–1900s] a female hairstyle consisting of two plaits bunched on top of the head.

3. [1990s+] (US black) a large hoop ear-ring.