View synonyms for -on


  1. a suffix used in the names of subatomic particles ( gluon; meson; neutron ), quanta ( graviton ), and other minimal entities or components ( cistron; codon; magneton; photon ).


  1. a suffix used in the naming of inert gaseous elements:




[ on, awn ]


  1. so as to be or remain supported by or suspended from:

    Put your package down on the table.

    Hang your coat on the hook.

  2. so as to be attached to or unified with:

    Hang the picture on the wall.

    Paste the label on the package.

  3. so as to be a covering or wrapping for:

    Put the blanket on the baby.

    Put aluminum foil on the lamb chops before freezing them.

  4. in connection, association, or cooperation with; as a part or element of:

    to serve on a jury.

  5. so as to be a supporting part, base, backing, etc., of:

    a painting on canvas;

    mounted on cardboard;

    legs on a chair.

  6. (used to indicate place, location, situation, etc.):

    a scar on the face;

    the book on the table;

    a house on 19th Street.

  7. (used to indicate immediate proximity):

    a house on the lake;

    to border on absurdity.

  8. in the direction of:

    on the left;

    to sail on a southerly course.

  9. (used to indicate a means of conveyance or a means of supporting or supplying movement):

    on the wing;

    This car runs on electricity.

    Can you walk on your hands?

    I'll be there on the noon plane.

  10. by the agency or means of:

    drunk on wine;

    talking on the phone;

    I saw it on television.

  11. in addition to:

    millions on millions of stars.

  12. with respect or regard to (used to indicate the object of an action directed against or toward):

    Let's play a joke on him.

    Write a critical essay on Shakespeare.

  13. in a state or condition of; in the process of:

    on strike;

    The house is on fire!

  14. subject to:

    a doctor on call.

  15. engaged in or involved with:

    He's on the second chapter now.

  16. (used to indicate a source or a person or thing that serves as a source or agent):

    a duty on imported goods;

    She depends on her friends for encouragement.

  17. (used to indicate a basis or ground):

    on my word of honor;

    The movie is based on the book.

  18. (used to indicate risk or liability):

    on pain of death.

  19. (used to indicate progress toward or completion of an objective):

    We completed the project on budget.

  20. assigned to or occupied with:

    Who's on reception this afternoon?

    Let’s shoot this one with you on lighting, and her on sound.

  21. Informal. so as to disturb or affect adversely:

    My hair dryer broke on me.

  22. Informal. paid for by, especially as a treat or gift:

    Dinner is on me.

  23. taking or using as a prescribed measure, cure, or the like:

    The doctor had her on a low-salt diet.

  24. regularly taking or addicted to:

    He was on drugs for two years.

  25. Informal. with; carried by:

    I have no money on me.

  26. (used to indicate time or occasion):

    on Sunday;

    We demand cash on delivery.

  27. (used to indicate the object or end of motion):

    to march on the capital.

  28. (used to indicate the object or end of action, thought, desire, etc.):

    to gaze on a scene.

  29. (used to indicate subject, reference, or respect):

    views on public matters.

  30. (used to indicate an encounter):

    The pickpocket crept up on a victim.

  31. (used to indicate fault or responsibility):

    It's on them to make their needs known.

    If you eat that and get sick, it's on you—I warned you!


  1. in, into, or onto a position of being supported or attached:

    Sew the buttons on.

  2. in, into, or onto a position of covering or wrapping:

    Put your raincoat on.

  3. fast to a thing, as for support:

    Hold on!

  4. toward a place, point, activity, or object:

    to look on while others work.

  5. forward, onward, or along, as in any course or process:

    further on.

  6. with continuous activity:

    to work on.

  7. into or in active operation or performance:

    Turn the gas on.


  1. operating or in use:

    The television set was on.

    Is your brake on?

  2. taking place; occurring:

    Don't you know there's a war on?

  3. performing or broadcasting:

    The radio announcer told us we were on.

  4. Informal.
    1. behaving in a theatrical, lively, or ingratiating way:

      Around close friends, one doesn't have to be on every minute.

    2. functioning or performing at one's best:

      When she's on, no other tennis player is half as good.

  5. scheduled or planned:

    Anything on after supper?

  6. Baseball. positioned on a base or bases:

    They had two men on when he hit the home run.

  7. Cricket. noting that side of the wicket, or of the field, on which the batsman stands.


  1. Cricket. the on side.



[ on ]


  1. Biblical name of Heliopolis.



abbreviation for

  1. Old Norse ( def ). Also ON., O.N.
  2. Ontario, Canada (approved for postal use).



abbreviation for

  1. Old Norse
  2. (esp in postal addresses) Ontario



/ ɒn /


  1. the ancient Egyptian and biblical name for Heliopolis



suffix forming nouns

  1. indicating a chemical substance



  2. (in physics) indicating an elementary particle or quantum



  3. (in chemistry) indicating an inert gas



  4. (in biochemistry) a molecular unit





/ ɒn /


  1. in contact or connection with the surface of; at the upper surface of

    an apple on the ground

    a mark on the table cloth

  2. attached to

    a puppet on a string

  3. carried with

    I've no money on me

  4. in the immediate vicinity of; close to or along the side of

    a house on the sea

    this verges on the ridiculous!

  5. within the time limits of a day or date

    he arrived on Thursday

  6. being performed upon or relayed through the medium of

    what's on the television?

  7. at the occasion of

    on his retirement

  8. used to indicate support, subsistence, contingency, etc

    he lives on bread

    it depends on what you want

    1. regularly taking (a drug)

      she's on the pill

    2. addicted to

      he's on heroin

  9. by means of (something considered as a mode of transport) (esp in such phrases as on foot, on wheels, on horseback, etc)
  10. in the process or course of

    on a journey

    on strike

  11. concerned with or relating to

    a programme on archaeology

    a tax on potatoes

  12. used to indicate the basis, grounds, or cause, as of a statement or action

    I have it on good authority

  13. against: used to indicate opposition

    they marched on the city at dawn

  14. used to indicate a meeting or encounter

    he crept up on her

  15. used with an adjective preceded by the indicating the manner or way in which an action is carried out

    on the cheap

    on the sly

  16. informal.
    1. staked or wagered as a bet

      ten pounds on that horse

    2. charged to

      the drinks are on me

  17. usually followed by it drinking alcoholic liquor
  18. informal.
    to the loss or disadvantage of

    the old car gave out on us


  1. in the position or state required for the commencement or sustained continuation, as of a mechanical operation

    the radio's been on all night

  2. attached to, surrounding, or placed in contact with something

    the girl had nothing on

  3. taking place

    what's on tonight?

  4. in a manner indicating continuity, persistence, concentration, etc

    the play went on all afternoon

    don't keep on about it

  5. in a direction towards something, esp forwards; so as to make progress

    march on!

    we drove on towards London

  6. on and off or off and on
    intermittently; from time to time
  7. on and on
    without ceasing; continually


  1. functioning; operating

    turn the switch to the on position

  2. informal.
    1. performing, as on stage

      I'm on in five minutes

    2. definitely taking place

      their marriage is still on

      the match is on for Friday

    3. tolerable, practicable, acceptable, etc

      your plan just isn't on

    4. (of a person) willing to do something
  3. on at informal.

    she was always on at her husband

  4. cricket (of a bowler) bowling


  1. cricket
    1. modifier relating to or denoting the leg side of a cricket field or pitch

      an on drive

      the on side

    2. in combination used to designate certain fielding positions on the leg side



Discover More

Word History and Origins

Origin of -on1

Probably extracted from ion; proton

Origin of -on2

Greek -on, neuter of -os adj. ending

Origin of -on3

First recorded before 900; Middle English on, an, Old English: “on, in, to”; cognate with Dutch aan, German an, Old Norse ā, Gothic ana; akin to Greek aná “up, upon” ( ana- )

Discover More

Word History and Origins

Origin of -on1

from ion

Origin of -on2

Old English an, on; related to Old Saxon an, Old High German, Gothic ana

Discover More

Idioms and Phrases

  1. on and off, off ( def 54a ).
  2. on and on, at great length, so as to become tiresome:

    They rambled on and on about their grandchildren.

  3. on the bow, Nautical. bow 3( def 8 ).
  4. on to, aware of the true nature, motive, or meaning of:

    I'm on to your little game.

Discover More

Example Sentences

Just the hard-on before you shoot unarmed members of the public.

Three on-the-record stories from a family: a mother and her daughters who came from Phoenix.

You just travel light with carry-on luggage, go to cities that you love, and get to hang out with all your friends.

It was a brick wall that we turned into the on-ramp of a highway.

Could the (thus far) timid trembling give way to a full-on, grand mal seizure?

I drew back from the rim of Writing-On-the-Stone, that set of whispered phrases echoing in my ears.

Kingston-on-Thames is still provincial in appearance, though now the centre of a great growth of modern suburbs.

Besides the districts mentioned, tobacco is grown largely in that of Frankfort-on-the Oder.

Madame Malmaison had always been a little proud of the beauty and grace and sweetness of her fitter-on.

Berwick-on-Tweed lies partly in England and partly in Scotland, the river which runs through it forming the boundary line.


Definitions and idiom definitions from Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.