The Collaborative International Dictionary of English v.0.48:

Hedgehog \Hedge"hog`\, n.
   1. (Zool.) A small European insectivore (Erinaceus
      Europ[ae]us), and other allied species of Asia and
      Africa, having the hair on the upper part of its body
      mixed with prickles or spines. It is able to roll itself
      into a ball so as to present the spines outwardly in every
      direction. It is nocturnal in its habits, feeding chiefly
      upon insects.
      [1913 Webster]

   2. (Zool.) The Canadian porcupine.[U.S]
      [1913 Webster]

   3. (Bot.) A species of Medicago (Medicago intertexta),
      the pods of which are armed with short spines; --
      popularly so called. --Loudon.
      [1913 Webster]

   4. A form of dredging machine. --Knight.
      [1913 Webster]

   5. (Elec.) A variety of transformer with open magnetic
      circuit, the ends of the iron wire core being turned
      outward and presenting a bristling appearance, whence the
      name.
      [Webster 1913 Suppl.]

   6. (Mil.) a defensive obstacle having pointed barbs extending
      outward, such as one composed of crossed logs with barbed
      wire wound around them, or a tangle of steel beams
      embedded in concrete used to impede or damage landing
      craft on a beach; also, a position well-fortified with
      such defensive obstacles.
      [PJC]

   Hedgehog caterpillar (Zool.), the hairy larv[ae] of several
      species of bombycid moths, as of the Isabella moth. It
      curls up like a hedgehog when disturbed. See Woolly
      bear, and Isabella moth.

   Hedgehog fish (Zool.), any spinose plectognath fish, esp.
      of the genus Diodon; the porcupine fish.

   Hedgehog grass (Bot.), a grass with spiny involucres,
      growing on sandy shores; burgrass (Cenchrus
      tribuloides).

   Hedgehog rat (Zool.), one of several West Indian rodents,
      allied to the porcupines, but with ratlike tails, and few
      quills, or only stiff bristles. The hedgehog rats belong
      to Capromys, Plagiodon, and allied genera.

   Hedgehog shell (Zool.), any spinose, marine, univalve shell
      of the genus Murex.

   Hedgehog thistle (Bot.), a plant of the Cactus family,
      globular in form, and covered with spines
      (Echinocactus).

   Sea hedgehog. See Diodon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Medicago intertexta
    n 1: an annual of the Mediterranean area having spiny seed pods
         and leaves with dark spots [syn: Calvary clover,
         Medicago intertexta, Medicago echinus]