insensible (adj.)

c. 1400, "lacking the power to feel with the senses, numb, dazed" (now rare in this meaning), from Late Latin insensibilis "that cannot be felt," from in- "not" (see in- (1)) + sensibilis "having feeling: perceptible by the senses" (see sensible). Meaning "void of feeling, not susceptible to emotion or passion" is from 1610s. Meaning "incapable of being felt or perceived by the senses or the mind, so small or slight as to be imperceptible" is from late 14c. Compare insensate.