WordWeb Online

1. Weak in willpower, courage or vitality
   "He was a spineless man with hardly a mind of his own";
   - namby-pamby, gutless, wishy-washy
    
2. (zoology) lacking a backbone or spinal column
   "worms are an example of spineless animals";
   - invertebrate
    
3. Lacking spiny processes
   "spineless fins"
    
4. Lacking thorns
   - thornless

See also: unarmed, weak

Antonym: spinous

Encyclopedia: Spineless