The Collaborative International Dictionary of English v.0.48:

Invertebrate \In*ver"te*brate\, a. (Zool.)
   Destitute of a backbone; having no vertebr[ae]; of or
   pertaining to the Invertebrata. -- n. One of the
   Invertebrata.
   [1913 Webster]

   Age of invertebrates. See Age, and Silurian.
      [1913 Webster]

WordNet (r) 3.0 (2006):

invertebrate
    adj 1: lacking a backbone or spinal column; "worms are an
           example of invertebrate animals" [syn: invertebrate,
           spineless] [ant: vertebrate]
    n 1: any animal lacking a backbone or notochord; the term is not
         used as a scientific classification

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "invertebrate":
   Milquetoast, abulic, afraid, amphibian, aquatic, baby, big baby,
   biped, canine, cannibal, carnivore, chicken, chicken liver,
   cosmopolite, coward, cowardly, crustacean, crustaceous, crybaby,
   disorganized, doormat, dull tool, emasculate, faint, fainthearted,
   feeble, feebleminded, feline, forceless, fraid-cat, fraidy-cat,
   frail, funk, funker, gnawer, gutless wonder, herbivore, impotent,
   inadequate, ineffective, ineffectual, infirm, insectivore,
   jellyfish, lightweight, lily liver, mammal, mammalian, marsupial,
   marsupialian, meek soul, milksop, molluscan, mollycoddle, mouse,
   namby-pamby, nebbish, nonentity, omnivore, pansy, pantywaist,
   pliable, primate, protozoan, protozoic, pushover, quadruped,
   reptile, rodent, ruminant, sad sack, scaredy-cat, scavenger, sissy,
   softling, softy, sop, spineless, ungulate, varmint, vermin,
   vertebrate, weak, weak sister, weak-kneed, weak-minded,
   weak-willed, weakling, white feather, white liver