The word 'urchin' has a fascinating journey from a specific animal to a descriptor for a child. It originates from the Middle English 'urchon', borrowed from the Anglo-Norman 'herichun', which itself came from the Latin 'ericius', meaning 'hedgehog'. The connection to the spiny animal is direct and ancient, traceable back to a Proto-Indo-European root meaning 'to bristle'. The semantic shift to describe a mischievous, ragged child occurred in the 16th century, drawing a vivid metaphorical link between the unkempt, prickly appearance of a poor street child and the spiny, round-bodied hedgehog. Later, the term was reapplied in marine biology to name the spiny, globular 'sea urchin', completing a full circle back to its original animal-based meaning.

The modern English word 'urchin' is a simplex word derived from a single, indivisible root via Middle English and Anglo-Norman. Its core morpheme is the historical root 'urch-', which evolved from the Latin word for hedgehog.