Ontario (in official postal use)

Old Norse

physically in contact with and supported by (a surface)

on the table was a water jug

she was lying on the floor

a sign on the front gate

forming a distinctive or marked part of the surface of

a scratch on her arm

a smile on her face

having (the thing mentioned) as a topic; about

a book on careers

as a member of (a committee, jury, or other body)

they would be allowed to serve on committees

having (the thing mentioned) as a target, aim, or focus

five air raids on Schweinfurt

thousands marching on Washington

her eyes were fixed on his dark profile

(often followed by a noun without a determiner) having (the thing mentioned) as a medium for transmitting or storing information

put your ideas down on paper

stored on the client's own computer

in the course of (a journey)

he was on his way to see his mother

indicating the day or part of a day during which an event takes place

reported on September 26

on a very hot evening in July

engaged in

his attendant was out on errands

regularly taking (a drug or medicine)

he is on morphine to relieve the pain

paid for by

the drinks are on me

added to

a few pence on the electricity bill is nothing compared with your security

physically in contact with and supported by a surface

make sure the lid is on

indicating continuation of a movement or action

she burbled on

he drove on

and so on

(of an event) taking place or being presented

what's on at the May Festival

there's a good film on this afternoon

(of an electrical appliance or power supply) functioning

they always left the lights on

(of a performer) on stage

the leg side