The term 'IT CAN KNOCK YOU OUT' can be solved by the crossword solutions ETHER (5 letters), OPIATE (6 letters), and ANESTHESIA (10 letters). ETHER is a colorless volatile liquid with a characteristic odor that was once widely used as an anesthetic. OPIATE is a drug derived from opium, such as morphine or codeine, that is used to relieve pain. Anesthesia is a state of reduced sensitivity to pain or other sensation, induced by drugs or other agents. All three of these substances are used in medicine to reduce pain and induce unconsciousness.