The Collaborative International Dictionary of English v.0.48:

Urchin \Ur"chin\ ([^u]"ch[i^]n), n. [OE. urchon, irchon, a
   hedgehog, OF. ire[,c]on, eri[,c]on, heri[,c]on, herichon, F.
   h['e]risson, a derivative fr. L. ericius, from er a hedgehog,
   for her; akin to Gr. chh`r. Cf. Herisson.]
   [1913 Webster]
   1. (Zool.) A hedgehog.
      [1913 Webster]

   2. (Zool.) A sea urchin. See Sea urchin.
      [1913 Webster]

   3. A mischievous elf supposed sometimes to take the form a
      hedgehog. "We 'll dress [them] like urchins, ouphes, and
      fairies." --Shak.
      [1913 Webster]

   4. A pert or roguish child; -- now commonly used only of a
      boy.
      [1913 Webster]

            And the urchins that stand with their thievish eyes
            Forever on watch ran off each with a prize. --W.
                                                  Howitt.
      [1913 Webster]

            You did indeed dissemble, you urchin you; but
            where's the girl that won't dissemble for an
            husband?                              --Goldsmith.
      [1913 Webster]

   5. 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. --Knight.
      [1913 Webster]

   Urchin fish (Zool.), a diodon.
      [1913 Webster]