Urchin

noun

1. A mischievous child.
2. A street urchin, a child who lives, or spends most of their time, in the streets.
3. A sea urchin.
4. One of a pair in a series of small card cylinders arranged around a carding drum; so called from its fancied resemblance to the hedgehog.
5. A neutron-generating device that triggered the nuclear detonation of the earliest plutonium atomic bombs.