WordWeb Online

1. Incapable of physical sensation
   "insensible to pain"; "insensible earth"
    
2. Unaware of or indifferent to
   "insensible to the suffering around him"
   - unaffected
    
3. Barely able to be perceived
   "an almost insensible change"
   - indiscernible, undetectable
    
4. Unresponsive to stimulation
   "he lay insensible where he had fallen"
   - senseless

See also: anaesthetic [Brit, Cdn], anesthetic [N. Amer], asleep, benumbed, imperceptible, incognisant [Brit], incognizant, insensibility, insensibly, insensitive, numb, unaware, unconscious, unperceivable

Antonym: sensible