at once

• attonce (obsolete)

From at + once.

• (UK) IPA^(key): /ət ˈwʌns/

• Audio (AU)

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at once (not comparable)

1. (obsolete) In one group; together.
   • 1590, Edmund Spenser, The Faerie Queene, III.4:

     Those two great champions did attonce pursew / The fearefull damzell with incessany payns [...].

2. (idiomatic) At the same time; simultaneously.

   Can you pat your head and rub your belly at once?
   He tried to eat four cookies at once.

   • 2013 August 10, Lexington, “Keeping the mighty honest: A new wave of press barons should not allow newspapers to become niche products”, in The Economist‎, volume 408, number 8848:

     The [Washington] Post's proprietor through those turbulent [Watergate] days, Katharine Graham, held a double place in Washington’s hierarchy: at once regal Georgetown hostess and scrappy newshound, ready to hold the establishment to account.

   • 2014 September 26, Tom Payne, “Sapiens: a Brief History of Humankind by Yuval Noah Harari, review: 'urgent questions' [print version: The story of our species, 27 September 2014, p. R32]”, in The Daily Telegraph (Review)‎:

     [T]he book, constructed in short, lucid episodes, can be satisfyingly read as a sequence of provocative talks, at once well informed and vatic.

3. (idiomatic) Immediately; now; right away.

   Tell the doctor to come at once. She is having a baby.

   • 1898, Winston Churchill, chapter 4, in The Celebrity:

     Mr. Cooke at once began a tirade against the residents of Asquith for permitting a sandy and generally disgraceful condition of the roads. So roundly did he vituperate the inn management in particular, and with such a loud flow of words, that I trembled lest he should be heard on the veranda.

   • 1918, W. B. Maxwell, chapter 3, in The Mirror and the Lamp:

     One saint's day in mid-term a certain newly appointed suffragan-bishop came to the school chapel, and there preached on “The Inner Life.”  He at once secured attention by his informal method, and when presently the coughing of Jarvis […] interrupted the sermon, he altogether captivated his audience with a remark about cough lozenges being cheap and easily procurable.

   • 1963, Margery Allingham, chapter 19, in The China Governess‎:

     As soon as Julia returned with a constable, Timothy, who was on the point of exhaustion, prepared to give over to him gratefully. The newcomer turned out to be a powerful youngster, fully trained and eager to help, and he stripped off his tunic at once.

• Acteon, octane