The Collaborative International Dictionary of English v.0.48:

fiddlehead \fid"dle*head`\ n.
   1. any of several tall ferns of northern temperate regions
      having graceful arched fronds and sporophylls resembling
      ostrich plumes.

   Syn: ostrich fern, shuttlecock fern, Matteuccia
        struthiopteris, Pteretis struthiopteris, Onoclea
        struthiopteris.
        [WordNet 1.5]

   2. New World fern (Osmunda cinnamonea) having woolly
      cinnamon-colored spore-bearing fronds in early spring
      later surrounded by green fronds, called also fiddlehead
      fern; the early uncurling fronds are edible, and
      sometimes considered as a vegetable delicacy.

   Syn: cinnamon fern, fiddlehead fern, Osmunda cinnamonea.
        [WordNet 1.5]

   3. (Naut.) an ornament on a ship's bow, curved like the
      volute or scroll at the head of a violin. Sometimes it
      serves the function of a billhead.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Osmunda cinnamonea
    n 1: New World fern having woolly cinnamon-colored spore-bearing
         fronds in early spring later surrounded by green fronds;
         the early uncurling fronds are edible [syn: cinnamon
         fern, fiddlehead, fiddlehead fern, Osmunda
         cinnamonea]