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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.
immediately; right now. We must leave at once! You must come here at once; it is an emergency.
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]
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.
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.