turn on

verb

• To set a flow of fluid or gas running by rotating a tap or valve.

  "Turn on the tap"

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

  "Please turn on automatic updates."

• (of a device) To start operating; to power up, to become on.

  "My computer won't turn on."

• To fill with enthusiasm; to intoxicate, give pleasure to ( + to an object of interest or excitement).

  "Attractive packaging can turn buyers on to a product."

• To sexually arouse.
• To cause to take up drugs, especially hallucinogens.
• To violently rebel against; to suddenly attack (this is the intransitive verb turn, with on functioning as a preposition not as an adverbial particle).

  "Suddenly all his friends turned on him."

• 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).

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