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c.1400, "lacking the power to feel with the senses," from Latin insensibilis "that cannot be felt," from in- "not" (see in- (1)) + sensibilis (see sensible). Also sometimes in Middle English "incapable of being felt or perceived by the senses" (early 15c.). Meaning "unconscious" is attested from early 15c. See insensate.
insensible in·sen·si·ble (ĭn-sěn'sə-bəl)
Having lost consciousness, especially temporarily; unconscious.
Lacking physical sensation or the power to react, as to pain or cold; numb.