turn on

turn on (third-person singular simple present turns on, present participle turning on, simple past and past participle turned on)

1. (transitive) To set a flow of fluid or gas running by rotating a tap or valve. [from 19th c.]

   Turn on the tap

2. (transitive) To power up, to put into operation, to start, to activate (an appliance, light, mechanism, functionality etc.).

   Please turn the lights on so I can see what I'm reading.

   Please turn on automatic updates.

   • 2011 December 14, Steven Morris, “Devon woman jailed for 168 days for killing kitten in microwave”, in Guardian:

     Robins, of Torquay, had denied a single charge of causing unnecessary suffering to an animal. She claimed the microwave was accidentally turned on by one of the cats after the kitten got inside. But Knutton said the kitten was too small to even get onto the work surface.

3. (intransitive, of a device) To start operating; to power up, to become on. [from 19th c.]

   My computer won't turn on.

4. (transitive) To fill with enthusiasm; to intoxicate, give pleasure to ( + to an object of interest or excitement). [from 20th c.]

   Attractive packaging can turn buyers on to a product.

   Attractive showroom models can turn buyers on

5. (transitive) To sexually arouse. [from 20th c.]
6. (transitive, slang) To cause to take up drugs, especially hallucinogens.
   • 1976, Robert H. Coombs, Lincoln J. Fry, Patricia G. Lewis, Socialization in drug abuse

     In fact, many youngsters will not even turn on a close friend if they know he has never used drugs. And it is rare indeed for a youth to actively seek out people to turn on.

7. (intransitive) To violently rebel against; to suddenly attack (this is the intransitive verb turn, with on functioning as a preposition not as an adverbial particle). [from 19th c.]

   Suddenly all his friends turned on him.

   • 2011 December 14, Angelique Chrisafis, “Rachida Dati accuses French PM of sexism and elitism”, in Guardian:

     She was Nicolas Sarkozy's pin-up for diversity, the first Muslim woman with north African parents to hold a major French government post. But Rachida Dati has now turned on her own party elite with such ferocity that some have suggested she should be expelled from the president's ruling party.

8. (intransitive) To depend upon; to pivot around, to have as a central subject (this is the intransitive verb turn, with on functioning as a preposition not as an adverbial particle). [from 17th c.]

   The argument turned on the question of whether or not jobs would be lost.

• In senses 1-6 turn on is a phrasal verb with on functioning as an adverbial particle. If the sense is transitive and the object is a noun, the particle on may feature before or after the noun. If the object is a personal pronoun, then the particle on must come after it.
• In senses 7-8, turn on comprises the verb turn used intransitively and on functioning as a preposition before a noun or pronoun.

• turn
• turn-on
• turn against

• turn off (senses 1 to 5 inclusive)

• untorn