At Once Meaning

(idiomatic) Immediately; now; right away.

Example: 1590, Edmund Spenser, The Faerie Queene, III.4:
  Those two great champions did attonce pursew / The fearefull damzell with incessany payns [...].
  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”[1], 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]”[2], 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.
  Tell the doctor to come at once. She is having a baby.‎
1898, Winston Churchill, chapter 4, 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, 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, The China Governess[3]:
  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.