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1. Immediately. I need you to call me at once—we have an urgent matter to discuss. The boss wants you to start working on this report at once.
2. At the same time. Don't try to carry more than two boxes at once—they're heavy! I can't understand a word with all of you screaming at once.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
immediately; right now. We must leave at once! You must come here at once; it is an emergency.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
1. At the same time, as in We can't all fit into the boat at once. [First half of 1200s] Also see at one time, def. 1.
2. Immediately, as in Mother told the children to come inside at once. [First half of 1500s]
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
1 immediately: I’m afraid there’s a problem. I must ask you to leave the building at once.
2 at the same time: Don’t all speak at once! ♢ I’m not superwoman, you know. I can’t do a hundred things at once.
Farlex Partner Idioms Dictionary © Farlex 2017
1. All at one time; simultaneously: Everything happened at once. The view of the skyline is at once awesome, grand, and disappointing.
2. Immediately; instantly: Leave the room at once.
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.