at one

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1. Being a single entity, unit, object, or living being: I ate one peach.
2. Characterized by unity; undivided: They spoke with one voice.
a. Of the same kind or quality: two animals of one species.
b. Forming a single entity of two or more components: three chemicals combining into one solution.
4. Being a single member or element of a group, category, or kind: I'm just one player on the team.
5. Being a single thing in contrast with or relation to another or others of its kind: One day is just like the next.
6. Occurring or existing as something indefinite, as in time or position: He will come one day.
7. Occurring or existing as something particular but unspecified, as in time past: late one evening.
8. Informal Used as an intensive: That is one fine dog.
9. Being the only individual of a specified or implied kind: the one person I could marry; the one horse that can win this race.
1. The cardinal number, represented by the symbol 1, designating the first unit in a series.
2. A single person or thing; a unit: This is the one I like best. Of her many books, the best ones are the last two.
3. A one-dollar bill.
1. An indefinitely specified individual: She visited one of her cousins.
2. An unspecified individual; anyone: "The older one grows the more one likes indecency" (Virginia Woolf).
at one
In accord or unity.
one and all
one by one
Individually in succession.

[Middle English on, from Old English ān; see oi-no- in Indo-European roots.]
Usage Note: In formal usage, the pronoun one is sometimes used as a generic pronoun meaning "anyone": One would hope that train service could be improved. The informal counterpart of one is you: You never know what to expect from her. Trouble arises when one is used in a series of sentences, and there is a need for a relative pronoun to refer back to one. One option is to use one and one's repeatedly, as in One tries to be careful about where one invests one's money. But in a sequence of sentences this inevitably becomes tedious. A traditional alternative has been to use he, him, and his: One tries to be careful about his investments. This has the drawback of raising the specter of gender bias. Because of these problems, the temptation may arise to switch to you, but this will undoubtedly be distracting to the reader. It is better to use the same generic pronoun throughout. · As a generic pronoun, one should be avoided as the direct object of a verb or a preposition, especially if it comes at the end of the sentence. Thus the sentence Bad dreams can make one restless may sound stilted, but One must not tease the bears or they will attack one sounds almost ungrammatical. As a subject or in the possessive form, one fares much better. One should be cordial with one's colleagues sounds somewhat formal, but is acceptable. · Does the phrase One of x, where x is a plural noun phrase, take a singular or a plural verb? Sometimes the answer is straightforward. In the sentence One of every ten rotors was found defective, the one defective rotor is contrasted with, rather than being an example of, the larger group of rotors. A singular verb is almost always used here because it agrees with the singular "one." In 2001, 99 percent of the Usage Panel accepted the singular verb in this sentence. In many cases, the contrastive use of one of can be easily identified by the fact that the phrase containing one is introduced by the definite article: He is the only one of the students who has (not have) already taken Latin. Constructions such as one of those people who are more problematic. In the sentence He is one of those men who are constantly complaining about their jobs, the one man, rather than being in contrast to the larger group, is an example of a larger group of men who complain. The relative pronoun who appears to refer to men, and so the verb should be plural: are. But the use of a singular verb in sentences like these has long been common, even among the best writers, presumably because the relative clause, though semantically modifying the adjacent noun (men), feels like it fits equally well with the subject noun (he). The Usage Panel, accordingly, does not have a strict preference for the plural form. In our 2014 survey, although 72 percent accepted the plural are constantly complaining, 57 percent accepted the singular is constantly complaining. In some cases the Panel actually preferred the supposedly incorrect singular: 64 percent accepted The sports car turned out to be one of the most successful products that was ever manufactured in this country, while only 55 percent accepted were ever manufactured. Several Panelists commented that they decide by ear which verb form to use, and that appears to be the most viable advice. In some (but not all) cases, the sentence can be rewritten to avoid the choice: The sports car turned out to be one of the most successful products ever manufactured in this country. · Constructions using one or more or one or two always take a plural verb: One or more cars were parked in front of the house each day this week. One or two students from our department have won prizes. Note that when followed by a fraction, one ordinarily gets a plural verb: One and a half years have passed since I last saw her. The fraction rule has an exception in that amounts are sometimes treated as singular entities: One and a half cups is enough sugar. Note also that the plural rule does not apply to these one-plus-a-fraction constructions that are introduced by the indefinite article. These constructions are always singular: A year and a half has passed since I last saw her. See Usage Note at he1.
Word History: Why do we pronounce one (wŭn) and once (wŭns) while other words derived from one, like only, alone, and atone, are pronounced with a long o? Over time, stressed vowels commonly become diphthongs, as when Latin bona, the feminine singular of the adjective meaning "good," became buona in Italian and buena in Spanish. A similar diphthongization of one and once began in the late Middle Ages in the west of England and in Wales and is first recorded around 1400. The vowel sound underwent a series of changes, such that the word's pronunciation went from (ōn) to (o͞oōn), with two syllables, to (wōn) to (wo͞on) to (wo͝on) and finally to (wŭn). In southwest England, this diphthongization happened to other words beginning with the long o sound, such as oats, pronounced there now as (wŭts). Only in one and once did this diphthongal pronunciation gain widespread usage.
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.
References in classic literature ?
One sits by one's self, it is true, but one thinks; one opens one's favorite book and reads one's favorite story; one speaks to one's aunt or one's brother, fondles one's cat, or looks at one's photograph album.
This talk went in at one ear and out at the other, for a boy who spends his life eating and sleeping does not worry about anything till it actually stares him in the face.
By this means we can theoretically collect together a number of particulars which may be defined as the "aspects" or "appearances" of one thing at one time.
This gives us, so far, only those particulars which constitute one thing at one time.
To illustrate by the case of an actor on the stage: our first plan was to collect together all the aspects which he presents to different spectators at one time, and then to form the series of such sets.
At one lecture two Japanese gentlemen were induced to talk to one another in their own language, via the telephone.