on / än; ôn/ • prep. 1. 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. ∎  located somewhere in the general surface area of (a place): an internment camp on the island the house on the corner. ∎  as a result of accidental physical contact with: one of the children had cut a foot on some glass he banged his head on a beam. ∎  supported by (a part of the body): he was lying on his back. ∎  so as to be supported or held by: put it on the table. ∎  in the possession of (the person referred to): she only had a few dollars on her. 2. forming a distinctive or marked part of (the surface of something): a scratch on her arm a smile on her face. 3. having (the thing mentioned) as a topic: a book on careers essays on a wide range of issues. ∎  having (the thing mentioned) as a basis: modeled on the Mayflower Compact dependent on availability. 4. as a member of (a committee, jury, or other body): they would be allowed to serve on committees. 5. having (the place or thing mentioned) as a target: five air raids on the city thousands marching on Washington. ∎  having (the thing mentioned) as a target for visual focus: her eyes were fixed on his dark profile. 6. 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. ∎  being broadcast by (a radio or television channel): a new TV series on Channel 4. 7. in the course of (a journey): he was on his way to see his mother. ∎  while traveling in (a public conveyance): John got some sleep on the plane. ∎  on to (a public conveyance) with the intention of traveling in it: we got on the train. 8. 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. ∎  at the time of: she was booed on arriving home. 9. engaged in: his attendant was out on errands. 10. regularly taking (a drug or medicine): he is on morphine to relieve the pain. 11. paid for by: the drinks are on me. 12. added to: a few cents on the electric bill is nothing compared with your security.• adv. 1. physically in contact with and supported by a surface: make sure the lid is on. ∎  (of clothing) being worn by a person: sitting with her coat on get your shoes on. 2. indicating continuation of a movement or action: she burbled on he drove on and so on. ∎  further forward; in an advanced state: later on time's getting on. 3. (of an entertainment or other event) taking place or being presented: what's on at the festival there's a good film on this afternoon. ∎  due to take place as planned: the reorganization is still on. 4. (of an electrical appliance or power supply) functioning: they always left the lights on. ∎  (of a performer, etc.) broadcasting or acting. ∎  (of an employee) working.PHRASES: be on about Brit., inf. talk about tediously and at length: she's always on about doing one's duty.it's not on inf., chiefly Brit. it's impractical or unacceptable.on and off intermittently: it rained on and off most of the afternoon.on and on continually; at tedious length: he went on and on about his grandad's trombone.what are you on? inf. said to express incredulity at someone's behavior, with the implication that they must be under the influence of drugs.you're on inf. said by way of accepting a challenge or bet.

on prep. and adv. expressing the relation of contact with or proximity to a surface (hence with implication of support by it) and motion to or toward a position (later often expressed by on to, onto XVI); in early use covering also some of the uses now expressed by in and at. OE. on, orig. unstressed var. of an = OS., OHG. ana, an (Du. aan, G. an), ON. á, Goth. ana, rel. to Gr. aná, ána on, upon, Skr. ā up, Av. ana, OSl. na.
Hence onward(s) XVI.

ON¹ • abbr. Ontario (in official postal use).