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adverb, preposition by pronunciation in American English /baɪ/
By can be used in the following ways:
as a preposition (followed by a noun): The building was destroyed by fire.
as an adverb (without a following noun): As time went by, things improved.
 
  1. 1
    used for saying who or what does something
    1. a.
      used, especially with passive verbs, for showing who does something or what causes something

      Injured refugees were treated by a Red Cross doctor.

      Hull House was founded by Jane Addams in 1889.

      Children are fascinated by the idea of magic.

      The fabric had been faded by the sun.

      a rebellion by separatist guerrilla forces

    2. b.
      used for saying who wrote a book or a piece of music, who painted a picture, etc.

      a novel by Graham Greene

      mural paintings by Diego Rivera

  2. 2
    used for saying how something is done
    1. a.
      using a particular method to achieve something

      Reading is taught by traditional methods here.

      The palace balcony is shielded by bulletproof glass.

      Every bit of lace is made by hand (=not using a machine).

      by doing something:

      By using the Internet you can do your shopping from home.

      by mail/phone/fax etc.:

      They exchanged New Year's greetings by e-mail.

      We'll send you the tickets by mail.

    2. b.
      using a particular method of transportation
      by car/train/bus/air etc.:

      Sophie's parents arrived by taxi.

    3. c.
      using a particular road, path, door, etc.

      We returned home by a different route.

      She went in by the side entrance.

    4. d.
      using a particular name or title

      Staff members generally address each other by their first name.

      The U.N. refugee agency is known by its initials UNHCR.

    5. e.
      used for saying how you start or finish something

      I'm going to start off by explaining the purpose of our campaign.

  3. 3
    before or until
    1. a.
      not later than a particular time or date

      The meeting should have finished by 4:30.

      Application forms must be received by March 31st.

    2. b.
      during the period until a particular time or date

      By mid afternoon over 5,000 people had visited the exhibition.

      by the time (that):

      By the time Charlotte was 15, she had already achieved worldwide fame.

  4. 4
    used when saying that something happens in a way that was not planned or intended

    Take care that you don't shoot one of us by mistake.

    We met quite by chance.

    By a stroke of luck I found the perfect title for my new book.

  5. 5
    used for saying that time passes, or how it passes

    As time went by, people's attitudes changed.

    The days seem to fly by.

    I find that Friday afternoons just drag by (=go very slowly).

  6. 6
    used for showing how much something has changed, or how much difference there is between things

    House prices rose by an average 23% last year.

    Owen broke the world record by 2.4 seconds.

    See also  far
  7. 7
    used for saying that someone or something goes past you

    She walked right by me without saying a word.

    There were angry shouts from the crowd as the president's motorcade drove by.

  8. 8
    beside or close to someone or something

    She was sitting over there by the window.

    There's an ashtray just by your elbow.

  9. 9
    according to rules or laws

    Casinos are forbidden by law to contribute to political campaigns.

    In the police force we have to do everything by the rulebook.

  10. 10
    used for showing that something is judged according to certain standards of behavior, quality, etc.

    It's no use trying to judge 18th-century morality by modern standards.

    Her performance was amazing by any standard.

  11. 11
    used for saying that someone stops somewhere for a short time, especially while going to another place
    drop/stop/come by:

    Why don't you stop by on your way home from work?

    Peggy dropped by the office this afternoon.

  12. 12
    used for saying which part of a person's body or thing you take in your hand when you hold them

    Taking me by the arm, she led me into the next room.

    Always pick up a CD by the outer edge to avoid damaging the surface.

  13. 13
    used for referring to someone's personality, job, origin, name, etc.
    by nature/profession/birth/name etc.:

    She was, by nature, a cheerful and friendly sort of person.

    An American by birth, Cassidy had spent much of his life in Bolivia.

  14. 14
    used in calculations and measurements math
    1. a.
      used for saying what units of measurement are used

      Floor coverings are priced by the square foot.

      Industrial workers are generally paid by the hour.

      sold by the dozen

    2. b.
      used for giving the size of an area, object, or space by stating its length, width, height, etc.

      The house has a spacious dining room, measuring 18 by 15 feet.

      I usually get 4 by 6 inch prints of my pictures.

  15. 15
    used for showing a gradual process
    1. a.
      used when saying that something happens or changes gradually
      little by little/bit by bit:

      Little by little Philip got used to life on the farm.

      day by day/week by week etc.:

      His medical condition is continuing to improve day by day.

    2. b.
      used when things or people do something or are dealt with one after the other
      one by one/stage by stage:

      One by one the men came forward to receive their medals.

      item by item:

      The finance committee checks through each document, item by item.

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