Incapable or deprived of physical sensation.
Unable to be perceived by the senses.
Incapable of mental feeling; indifferent.
Not sensible or reasonable; meaningless.
Incapable of emotional feeling; callous; apathetic.
Unable to be understood; unintelligible.
The natural inclination to do whatever is necessary to succeed (including extreme violence)
Used other than figuratively or idiomatically: see killer, instinct.