1.verbTo set a flow of fluid or gas running by rotating a tap or valve.
"Turn on the tap"
2.verbTo power up, to put into operation, to start, to activate (an appliance, light, mechanism, functionality etc.).
"Please turn on automatic updates."
3.verb(of a device) To start operating; to power up, to become on.
"My computer won't turn on."
4.verbTo fill with enthusiasm; to intoxicate, give pleasure to ( + to an object of interest or excitement).
"Attractive packaging can turn buyers on to a product."
5.verbTo sexually arouse.
6.verbTo cause to take up drugs, especially hallucinogens.
7.verbTo 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."
8.verbTo 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."