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-on 1

a. A discrete, small unit, such as a subatomic particle: baryon.
b. A property of a physical system when quantized as a particle: phonon.
2. A sequence of nucleotides or region of DNA: codon.

[From (electr)on (influenced by Greek -on, neuter of -os, n. and adj. suff., and -on, neuter of -ōn, n. and adj. suff.)]

-on 2

Inert gas: radon.

[New Latin, from (arg)on.]

-on 3

A chemical compound that is not a ketone or a compound that contains oxygen in a carbonyl group: parathion.

[Alteration of -one.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


suffix forming nouns
1. (Chemistry) indicating a chemical substance: interferon; parathion.
2. (General Physics) (in physics) indicating an elementary particle or quantum: electron; photon.
3. (Chemistry) (in chemistry) indicating an inert gas: neon; radon.
4. (Biochemistry) (in biochemistry) a molecular unit: codon; operon.
[from ion]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ɒn, ɔn)

1. so as to be or remain supported by or suspended from: Put the package on the table. Hang your coat on the hook.
2. so as to be attached to or unified with: a label on a jar.
3. so as to be a covering or wrapping for: Put the blanket on the baby.
4. in connection, association, or cooperation with: to serve on a jury.
5. so as to be a supporting part or base of: legs on a chair.
6. having as a place, location, situation, etc.: a scar on the face; a store on 19th Street.
7. in immediate proximity to: a house on the lake.
8. in the direction of: to sail on a southerly course.
9. using as a means of conveyance or of supporting or supplying movement: arriving on the noon plane; a car that runs on electricity.
10. by the agency or means of: drunk on wine; talking on the phone.
11. directed against or toward: played a joke on him.
12. having as a subject; about: a book on birds.
13. in a state, condition, or process of: on strike.
14. engaged in or involved with: I'm on the second chapter now.
15. subject to: a doctor on call.
16. having as a source or agent: to depend on friends for support.
17. having as a basis or ground: on my word of honor.
18. assigned to or working at: Who's on the switchboard today?
19. at the time or occasion of: on Sunday; cash on delivery.
20. within the required limits of: on time.
21. having as the object or end of motion: to march on the capital; to creep up on someone.
22. having as the object or end of action, thought, desire, etc.: to gaze on a scene.
23. having as the subject or reference; with respect to: views on public matters.
24. paid for by, esp. as a treat or gift: Dinner is on me.
25. taking or using as a prescribed measure, cure, etc.: on a low-salt diet.
26. regularly taking or addicted to: on drugs.
27. with; carried by: I have no money on me.
28. so as to disturb or affect adversely: My hair dryer broke on me.
29. having as a risk or liability: on pain of death.
30. in addition to: millions on millions of stars.
31. in, into, or onto a position of being supported or attached: Sew the buttons on.
32. in, into, or onto a position of covering or wrapping: Put your raincoat on.
33. fast to a thing, as for support: Hold on!
34. toward a place, point, activity, or object: to look on while others work.
35. forward, onward, or along, as in any course or process: further on.
36. with continuous activity: to work on.
37. into or in active operation or performance: Turn the gas on.
38. operating or in use: Is the radio on?
39. taking place; occurring: Don't you know there's a war on?
40. performing or broadcasting: The radio announcer told us we were on.
a. behaving in a very animated or theatrical manner.
b. functioning or performing at one's best.
42. scheduled or planned: Anything on tonight?
1. on and off, off (def. 46).
2. on and on, at great length, so as to become tiresome.
[before 900; Middle English on, an, Old English: on, in, to, c. Old Frisian, Old Saxon an(a), Old High German an(a), Old Norse ā-, Gothic ana; akin to Greek aná up, upon (see ana-)]


1. Old Norse.
2. Ontario, Canada.


a suffix used in the names of subatomic particles (gluon; neutron), quanta (graviton), and other minimal entities or components (codon; magneton; photon).
[probably extracted from ion; compare proton]


a suffix used in the names of inert gaseous elements: neon.
[« Greek -on, neuter of -os adj. ending]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.