The Collaborative International Dictionary of English v.0.48:

Silkworm \Silk"worm`\, n. [AS. seolcwyrm.] (Zool.)
   The larva of any one of numerous species of bombycid moths,
   which spins a large amount of strong silk in constructing its
   cocoon before changing to a pupa.
   [1913 Webster]

   Note: The common species (Bombyx mori) feeds on the leaves
         of the white mulberry tree. It is native of China, but
         has long been introduced into other countries of Asia
         and Europe, and is reared on a large scale. In America
         it is reared only to small extent. The Ailanthus
         silkworm (Philosamia cynthia) is a much larger
         species, of considerable importance, which has been
         introduced into Europe and America from China. The most
         useful American species is the Polyphemus. See
         Polyphemus.
         [1913 Webster]

   Pernyi silkworm, the larva of the Pernyi moth. See Pernyi
      moth.

   Silkworm gut, a substance prepared from the contents of the
      silk glands of silkworms and used in making lines for
      angling. See Gut.

   Silkworm rot, a disease of silkworms; muscardine.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Caterpillar \Cat"er*pil`lar\, n. [OE. catyrpel, corrupted fr.
   OF. chatepelouse, or cate pelue, fr. chate, F. chatte,
   she-cat, fem. of chat, L. catus + L. pilosus hairy, or F.
   pelu hairy, fr. L. pilus hair. See Cat, and Pile hair.]
   1. (Zool.) The larval state of a butterfly or any
      lepidopterous insect; sometimes, but less commonly, the
      larval state of other insects, as the sawflies, which are
      also called false caterpillars. The true caterpillars have
      three pairs of true legs, and several pairs of abdominal
      fleshy legs (prolegs) armed with hooks. Some are hairy,
      others naked. They usually feed on leaves, fruit, and
      succulent vegetables, being often very destructive, Many
      of them are popularly called worms, as the cutworm,
      cankerworm, army worm, cotton worm, silkworm.
      [1913 Webster]

   2. (Bot.) A plant of the genus Scorpiurus, with pods
      resembling caterpillars.
      [1913 Webster]

   Caterpillar catcher, or Caterpillar eater (Zool.), a bird
      belonging to the family of Shrikes, which feeds on
      caterpillars. The name is also given to several other
      birds.

   Caterpillar hunter (Zool.), any species of beetles of the
      genus Callosoma and other allied genera of the family
      Carabid[ae] which feed habitually upon caterpillars.
      [1913 Webster]

WordNet (r) 3.0 (2006):

silkworm
    n 1: the commercially bred hairless white caterpillar of the
         domestic silkworm moth which spins a cocoon that can be
         processed to yield silk fiber; the principal source of
         commercial silk
    2: larva of a saturniid moth; spins a large amount of strong
       silk in constructing its cocoon [syn: silkworm, giant
       silkworm, wild wilkworm]