The Collaborative International Dictionary of English v.0.48:

Porcupine \Por"cu*pine\, n. [OE. porkepyn, porpentine, OF.
   porc-espi, F. porc-['e]pic (cf. It. porco spino, porco
   spinoso, Sp. puerco espino, puerco espin, fr. L. porcus swine
   + spina thorn, spine). The last part of the French word is
   perhaps a corruption from the It. or Sp.; cf. F. ['e]pi ear,
   a spike of grain, L. spica. See Pork, Spike a large nail,
   Spine.]
   1. (Zool.) Any Old Word rodent of the genus Hystrix, having
      the back covered with long, sharp, erectile spines or
      quills, sometimes a foot long. The common species of
      Europe and Asia (Hystrix cristata) is the best known.
      [1913 Webster]

   2. (Zool.) Any species of Erethizon and related genera,
      native of America. They are related to the true
      porcupines, but have shorter spines, and are arboreal in
      their habits. The Canada porcupine (Erethizon dorsatus)
      is a well known species.
      [1913 Webster]

   Porcupine ant-eater (Zool.), the echidna.

   Porcupine crab (Zool.), a large spiny Japanese crab
      (Acantholithodes hystrix).

   Porcupine disease (Med.). See Ichthyosis.

   Porcupine fish (Zool.), any plectognath fish having the
      body covered with spines which become erect when the body
      is inflated. See Diodon, and Globefish.

   Porcupine grass (Bot.), a grass (Stipa spartea) with
      grains bearing a stout twisted awn, which, by coiling and
      uncoiling through changes in moisture, propels the
      sharp-pointed and barbellate grain into the wool and flesh
      of sheep. It is found from Illinois westward. See
      Illustration in Appendix.

   Porcupine wood (Bot.), the hard outer wood of the cocoa
      palm; -- so called because, when cut horizontally, the
      markings of the wood resemble the quills of a porcupine.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Echidna \E*chid"na\ ([-e]*k[i^]d"n[.a]), n. [L., a viper, adder,
   Gr. 'e`chidna.]
   1. (Gr. Myth.) A monster, half maid and half serpent.
      [1913 Webster]

   2. (Zo["o]l.) A genus of Monotremata found in Australia,
      Tasmania, and New Guinea. They are toothless and covered
      with spines; -- called also porcupine ant-eater, and
      Australian ant-eater.
      [1913 Webster]