A child.
A mischievous child.
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.
A street urchin, a child who lives, or spends most of their time, in the streets.
A sea urchin.
A neutron-generating device that triggered the nuclear detonation of the earliest plutonium atomic bombs.