Etymology: Middle English on, an, from Old English ān; akin to Old High German ein one, Latin unus (Old Latin oinos), Sanskrit eka
Date: before 12th century
1. being a single unit or thing <one day at a time> 2. a. being one in particular <early one morning> b. being preeminently what is indicated <one fine person> 3. a. being the same in kind or quality <both of one species> b. (1) constituting a unified entity of two or more components <the combined elements form one substance> (2) being in agreement or union <am one with you on this> 4. a. some 1 <will see you again one day> b. being a certain individual specified by name <one John Doe made a speech> 5. only 2a <the one person she wanted to marry> II. noun Date: before 12th century 1. — see number table 2. the number denoting unity 3. a. the first in a set or series — often used with an attributive noun <day one> b. an article of clothing of a size designated one <wears a one> 4. a single person or thing <has the one but needs the other> 5. a one-dollar bill III. pronoun Date: 13th century 1. a certain indefinitely indicated person or thing <saw one of his friends> 2. a. an individual of a vaguely indicated group ; anyone at all <one never knows> b. — used as a third person substitute for a first person pronoun <I'd like to read more but one doesn't have the time> 3. a single instance of a specified action <felt like belting him one — John Casey> Usage: Sense 2a is usually a sign of a formal style. A formal style excludes the participation of the reader or hearer; thus one is used where a less formal style might address the reader directly <for the consequences of such choices, one has only oneself to thank — Walker Gibson>. This generic one has never been common in informal use in either British or American English, and people who start sentences with one often shift to another pronoun more natural to casual discourse <when one is learning the river, he is not allowed to do or think about anything else — Mark Twain>. Use of one to replace a first-person pronoun—sense 2b—has occasionally been criticized. It is more common in British English than in American <I'm watching this pretty carefully and I hope that the issue will come up in the Lords and one may be able to speak about it — Donald Coggan>.
New Collegiate Dictionary. 2001.