Urchin

Urchin is the old English term for hedgehog. As such, it is applied to many things that take a similar form to a hedgehog:

• Sea urchins are round and prickly like hedgehogs.
• Children (especially boys) that behave in an annoying manner are commonly called urchins. This comes from the scrunched-face appearance of both hedgehogs and unruly children.
• In old theater, urchin was a common name for an elf or fairy that took on a prickly appearance.

For a detailed etymology, see The Online Etymology Dictionary