The Collaborative International Dictionary of English v.0.48:

Spineless \Spine"less\, a.
   1. Having no spine, or vertebral column.
      [1913 Webster]

   2. Having no thorns or barbs.
      [PJC]

   3. lacking in strength of character; cowardly, in a physical
      or moral sense.
      [PJC]

WordNet (r) 3.0 (2006):

spineless
    adj 1: weak in willpower, courage or vitality [syn: namby-
           pamby, gutless, spineless, wishy-washy]
    2: lacking a backbone or spinal column; "worms are an example of
       invertebrate animals" [syn: invertebrate, spineless]
       [ant: vertebrate]
    3: lacking spiny processes; "spineless fins" [ant: spinous,
       spiny]
    4: lacking thorns [syn: thornless, spineless]