Source : Webster's Revised Unabridged Dictionary (1913)

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

   {Age of invertebrates}. See {Age}, and {Silurian}.

Source : WordNet®

invertebrate
     adj : lacking a backbone or spinal column; "worms are an example
           of invertebrate animals" [ant: {vertebrate}]

invertebrate
     n : any animal lacking a backbone or notochord; the term is not
         used as a scientific classification