<B>on, </B>preposition, adverb, adjective, noun.<DL COMPACT><DD><I>prep. </I> <B>1. </B>above and supported by. <BR> <I>Ex. to stand on one foot, to ride on a train. The book is on the table.</I> <DD><B> 2. </B>touching so as to cover or be around. <BR> <I>Ex. a blister on one's heel, shoes on one's feet, a ring on one's finger.</I> <DD><B> 3. </B>close to; near. <BR> <I>Ex. a house on the shore, to border on absurdity.</I> <DD><B> 4. </B>in the direction of; toward. <BR> <I>Ex. The invading soldiers marched on the Capitol.</I> <DD><B> 5. </B>against; upon. <BR> <I>Ex. The picture is on the wall.</I> <DD><B> 6. </B>by means of; by the use of. <BR> <I>Ex. to talk on the telephone. This news is on good authority.</I> <DD><B> 7. </B>in the condition of; in the process of; in the way of. <BR> <I>Ex. on duty, on half pay, on fire, on purpose, on sale.</I> <DD><B> 8. </B>at the time of; during. <BR> <I>Ex. They greeted us on our arrival.</I> <DD><B> 9. </B>concerning; in relation to; in connection with. <BR> <I>Ex. a book on animals, a poem on winter.</I> <DD><B> 10. </B>for the purpose of. <BR> <I>Ex. He went on an errand.</I> <DD><B> 11. </B>in addition to. <BR> <I>Ex. Defeat on defeat discouraged them.</I> <DD><B> 12. </B>among. <BR> <I>Ex. on a team. I am on the committee considering new members for our club.</I> <DD><B> 13. </B>indicating risk or liability. <BR> <I>Ex. on pain of death.</I> <DD><I>adv. </I> <B>1. </B>on something or someone. <BR> <I>Ex. The walls are up, and the roof is on. Put on a clean shirt.</I> <DD><B> 2. </B>to something. <BR> <I>Ex. Hold on, or you may fall.</I> <DD><B> 3. </B>toward something. <BR> <I>Ex. Some played; the others looked on.</I> <DD><B> 4. </B>farther. <BR> <I>Ex. March on.</I> <DD><B> 5. </B>in or into a condition, process, manner, or action. <BR> <I>Ex. Turn the gas on.</I> <DD><B> 6. </B>from a time; forward. <BR> <I>Ex. later on, from that day on.</I> <DD><I>adj. </I> <B>1. </B>taking place. <BR> <I>Ex. The race is on.</I> <DD><B> 2. </B>near. <BR> <I>Ex. the on side.</I> <DD><B> 3. </B>in operation; operating. <BR> <I>Ex. The radio is on. The brake is on.</I> <DD><B> 4. </B>(Cricket.) of or on the side of the wicket or the field on which the batsman stands. <DD><B> 5. </B>(British Slang.) <DD><B> a. </B>effective; working. <BR> <I>Ex. "So you see, old boy, that while I agree with you, denationalization just isn't on: Labour's made such a howling mess of these industries that no one in his senses would ever buy them back!" (Punch).</I> <DD><B> b. </B>knowing; aware. <BR> <I>Ex. Says Whiteley [aLondon painter] "Dylan is ... the most on person in America" (Time).</I> <DD><I>noun </I> (Cricket.) the on side <BR><I>expr. <B>and so on.</B> </I>See under <B>so</B> (1). <BR><I>expr. <B>have nothing on.</B> </I>See under <B>have.</B> <BR><I>expr. <B>have on.</B> </I>See under <B>have.</B> <BR><I>expr. <B>on and off,</B> </I>at some times and not at others; now and then. <BR> <I>Ex. He looked out of the window on and off.</I> <BR><I>expr. <B>on and on,</B> </I>without stopping. <BR> <I>Ex. The woman talked on and on throughout the whole afternoon.</I> <BR><I>expr. <B>on to,</B> </I>(Slang.) aware of the truth about. <BR> <I>Ex. Some of the kids are sweet, though I have a feeling they're on to me (Punch).</I> <BR><I>expr. <B>put on.</B> </I>See under <B>put</B> (1). </DL>
<A NAME="on">
<B>-on,</B><DL COMPACT><DD> (suffix.) <DD><B> 1. </B>(Physics.) <DD><B> a. </B>a nuclear particle, as in <I>neutron, dyon, parton.</I> <DD><B> b. </B>any unit particle or quantum of energy, as in <I>photon, graviton, exciton.</I> <DD><B> 2. </B>(Genetics.) a unit of genetic material, as in <I>operon, cistron.</I> <DD><B> 3. </B>(Chemistry.) a variant of <B>-one,</B> used for a compound that is not a ketone, as in <I>diuron.</I> </DL>
<A NAME="on">
<B>ON</B> (no periods), <B>O.N.,</B> or <B>ON.,</B><DL COMPACT><DD> Old Norse. </DL>
<A NAME="ona">
<B>Ona, </B>noun, pl. <B>-na</B> or <B>-nas.</B><DL COMPACT><DD> a member of a tribe of American Indians formerly living on the island of Tierra del Fuego at the southernmost tip of South America. <BR> <I>Ex. The Ona hunted the guanaco, a small wild relative of the llama (Charles Wagley).</I> </DL>
<A NAME="onagainoffagain">
<B>on-again off-again,</B> or <B>on-again-off-again, </B>adjective.<DL COMPACT><DD> that is not steadily pursued or carried out; wavering; faltering; inconclusive; unresolved. <BR> <I>Ex. The fund was meant to free economic aid from the jerking, jolting, on-again-off-again procedures imposed by the annual cycle of appropriations (Economist).</I> </DL>
<A NAME="onager">
<B>onager, </B>noun, pl. <B>-gri,</B> <B>-gers.</B><DL COMPACT><DD><B> 1. </B>a wild ass of the dry plains of western central Asia, light brownish with a black stripe along its back. <DD><B> 2. </B>an ancient and medieval machine of war for throwing stones. </DL>
<A NAME="onagraceous">
<B>onagraceous, </B>adjective.<DL COMPACT><DD> belonging to the evening-primrose family. </DL>
<A NAME="onandoff">
<B>on-and-off, </B>adjective. <B>=off-and-on.</B> <I>Ex. After on-and-off contract negotiations for several months, the union called a strike (Wall Street Journal).</I> </DL>
<B>onanist, </B>noun.<DL COMPACT><DD> a person who practices onanism. </DL>
<A NAME="onanistic">
<B>onanistic, </B>adjective.<DL COMPACT><DD> having to do with or characteristic of onanism. </DL>
<A NAME="onboard">
<B>on-board, </B>adjective.<DL COMPACT><DD> on or within a vehicle; installed aboard. <BR> <I>Ex. The Gemini 5 rendezvous experiment [was] the first to use an on-board computer linked with on-board radar (New York Times).</I> </DL>
<A NAME="once">
<B>once, </B>adverb, noun, conjunction, adjective.<DL COMPACT><DD><I>adv. </I> <B>1. </B>one time. <BR> <I>Ex. Read it once more. He comes once a day. A man can die but once (Shakespeare).</I> <DD><B> 2. </B>at some one time in the past; formerly. <BR> <I>Ex. a once powerful nation. That big man was once a little baby.</I> <DD><B> 3. </B>even a single time; ever. <BR> <I>Ex. if the facts once become known; once seen, never forgotten.</I> <DD><B> 4. </B>(Archaic.) at some future time. <BR> <I>Ex. meditating that she must die once (Shakespeare).</I> <DD><I>noun </I> a single occasion. <BR> <I>Ex. Once is enough. I think he might as well have favoured me this once (Shelley).</I> <DD><I>conj. </I> if ever; whenever. <BR> <I>Ex. Most boys like to swim once they have learned how. Once you cross the river you are safe.</I> <DD><I>adj. </I> former. <BR> <I>Ex. a once friend.</I> (SYN) quondam. <BR><I>expr. <B>all at once,</B> </I>suddenly. <BR> <I>Ex. All at once the sun disappeared and rain began to fall.</I> <BR><I>expr. <B>at once,</B> <DD><B> a. </B>immediately. </I> <I>Ex. You must come at once.</I> <DD><B> b. </B>at one and the same time. <BR> <I>Ex. All three boys spoke at once.</I> <BR><I>expr. <B>for once,</B> </I>for one time at least. <BR> <I>Ex. For once I wasn't thinking of you. I had other things in mind (Graham Greene).</I> <BR><I>expr. <B>once and again,</B> </I>repeatedly. <BR> <I>Ex. That good woman would open the door once and again in the morning, and put her head through (Mrs. Humphry Ward).</I> <BR><I>expr. <B>once</B> (<B>and</B>) <B>for all.</B> </I>See under <B>all.</B> <BR><I>expr. <B>once in a while.</B> </I>See under <B>while.</B> <BR><I>expr. <B>once or twice,</B> </I>a few times. <BR> <I>Ex. So the merchants ... lodged without Jerusalem once or twice (Nehemiah 13:20)</I> <BR><I>expr. <B>once upon a time.</B> </I>See under <B>time.</B> </DL>
<A NAME="onceover">
<B>once-over, </B>noun.<DL COMPACT><DD> (Informal.) a short, quick look, as for inspection or evaluation. <BR> <I>Ex. to give the new plans a quick once-over.</I> </DL>
<A NAME="onceoverlightly">
<B>once-over-lightly, </B>noun, adjective.<DL COMPACT><DD><I>noun </I> (Informal.) a light or superficial look, as for inspection or evaluation; a casual once-over. <BR> <I>Ex. The religious essays ... are a once-over-lightly in the principles of Catholicism (Time).</I> <DD><I>adj. </I> superficial; casual. <BR> <I>Ex. once-over-lightly coverage of the news.</I> </DL>
<A NAME="onchocerciasis">
<B>onchocerciasis, </B>noun.<DL COMPACT><DD> a tropical disease that causes nodules under the skin and lesions of the eye which may result in blindness; river blindness. It is caused by a filarial worm whose carrier is a gnat. </DL>
<A NAME="oncidium">
<B>oncidium, </B>noun.<DL COMPACT><DD> any one of a group of tropical American epiphytic orchids. Some kinds have flowers resembling butterflies. </DL>
<A NAME="oncogen">
<B>oncogen, </B>noun.<DL COMPACT><DD> a tumor-producing virus or other agent; oncogenic substance or organism. </DL>
<A NAME="oncogene">
<B>oncogene, </B>noun.<DL COMPACT><DD> a tumor-producing gene. <BR> <I>Ex. The theory itself states that human cancer is viral in origin and is caused by a more or less hypothetical entity called the oncogene (Harper's).</I> </DL>
<A NAME="oncogenesis">
<B>oncogenesis, </B>noun.<DL COMPACT><DD> the process of forming or producing tumors. </DL>
<A NAME="oncogenic">
<B>oncogenic, </B>adjective.<DL COMPACT><DD> having to do with or producing tumors; tending to produce tumors. </DL>
<A NAME="oncogenicity">
<B>oncogenicity, </B>noun.<DL COMPACT><DD> the quality or condition of being oncogenic. </DL>
<A NAME="oncologic">
<B>oncologic, </B>adjective. =oncological.</DL>
<A NAME="oncological">
<B>oncological, </B>adjective.<DL COMPACT><DD> of or having to do with oncology. <BR> <I>Ex. [Russia] has embarked on a nationwide specialist oncological service to deal with all growth disorders, benign and malignant (London Times).</I> </DL>
<A NAME="oncologist">
<B>oncologist, </B>noun.<DL COMPACT><DD> a person who studies, or knows much about, oncology. </DL>
<A NAME="oncology">
<B>oncology, </B>noun.<DL COMPACT><DD> the branch of medicine dealing with the study of tumors. </DL>
<A NAME="oncolytic">
<B>oncolytic, </B>adjective.<DL COMPACT><DD> of or having to do with the destruction of cells comprising a tumor. <BR> <I>Ex. oncolytic properties.</I> </DL>
<A NAME="oncoming">
<B>oncoming, </B>adjective, noun.<DL COMPACT><DD><I>adj. </I> approaching or advancing. <BR> <I>Ex. oncoming winter, the oncoming tide, oncoming traffic.</I> <DD><I>noun </I> approach; advance. <BR> <I>Ex. the oncoming of the storm; the oncoming of numbness (George Eliot).</I> </DL>