adj

• Happening; taking place; being or due to be put into action.
  ""Five bucks says the Cavs win tonight." ―"You're on!""
• (postpositive) Of a stated part of something, oriented towards the viewer or other specified direction.
  "The photograph shows the UFO side on."
• (chiefly UK, informal, chiefly in the negative) Acceptable, appropriate.
  "It's not fair to do that – it's just not on."
• (chiefly in the negative) Possible; capable of being successfully carried out.
  "Climbing up that steep ridge isn't on. We'll have to find another route."

adv

• (infrequent in the US) Later.
  "Ten years on, nothing had changed in the village."
• (snooker) Of a ball, into a pottable position.
  "The black was previously unavailable, but in potting that red, he's now pushed the black on."

prep

• Indicating position or location.
  "A ship was sighted on the port quarter."
• (UK) At (a certain value or level).
  "The Tories are on twenty-five percent in this constituency."
• (UK, especially in sports reporting) At (a given time after the start of something).
  "Smith scored again on twelve minutes, doubling Mudchester Rovers' lead."
• (informal) In the possession of.
  "I haven't got any money on me."

verb

• (Singapore, Philippines, Malaysia, Nigeria, transitive, colloquial) To switch on.
  "Can you on the light?"