Chin

Chin \chin\ , noun;

Chins are weird. For one thing, people are the only animals that have them. Think about it, other animals just have the bottom of their jaw while we have this jutting thing below that. Is it because we speak? Or does it have something to do with our unique diet? Or maybe sexual selection? The truth is, no one really knows but anthropologists love to debate it. There's an interesting overview here.

Another weird thing about chins is that we are extremely vain about them. Google image search chin and you will see tons of plastic surgeons' before and after pics, as well as plenty of devices to lift your chin or combat double-chins and the fat deposits underneath. There are also plenty of pictures like this to make you smile:

(source)

While the jury is out on the origin of our chin, the origin of the word is a little more certain. It is from Old English cin, which derives from a general Germanic word that comes from Proto-Indo-European *genu- ("chin, jawbone").