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Cause to begin the operation, flow, or activity of, as in Turn on the lights, please , or Don't turn on the sprinkler yet . [First half of 1800s]

Begin to display, employ, or exude, as in He turned on the charm . [Late 1800s]

Also, . Take or cause to take a mind-altering drug, as in The boys were excited about turning on , or They tried to get her high , or I told them I wouldn't get on tonight . [ Slang ; mid-1900s]

Be or cause to become excited or interested, as in His mother was the first to turn him on to classical music . [c. 1900]

Be or become sexually aroused, as in He blushed when she asked him what turned him on . [Second half of 1900s]

Also, turn upon . Depend on, relate to, as in The entire plot turns on mistaken identity . This usage, first recorded in 1661, uses turn in the sense of “revolve on an axis or hinge.”

Also, turn upon . Attack, become hostile toward, as in Although normally friendly, the dog suddenly turned on everyone who came to the door . Also see turn against .