at once
[adverb]
Synonyms: together, coincidentally, coincidently, coinstantaneously, concurrently, simultaneously, away, directly, first off, forthwith, immediately, instanter, instantly, now, right away, straightway

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English Thesaurus: immediately, at once, right away, instantly, right now/this minute, ...

[TahlilGaran] English Synonym Dictionary ▲

at once
immediately – used especially for emphasis

[TahlilGaran] Dictionary of Contemporary English ▲

immediately very soon after something else happens, and without any delay:
Sam immediately offered to help.
at once immediately – used especially for emphasis:
Remove the pie from the oven and serve at once.
He came home at once when he heard his wife was ill.
right away (also straightaway British English) especially spoken immediately, especially because something is urgent. Right away and straight away are less formal than immediately, and are very common in everyday spoken English:
If this happens, let us know right away.
I apologized straightaway.
instantly if something happens instantly, it happens immediately after something else, with almost no time between:
The boy was killed instantly.
The message is sent instantly from your computer.
right now/this minute spoken if someone orders you to do something right now, they want you to do it immediately, especially because they are annoyed with you:
The head teacher wants to see you right now.
without delay immediately, because it is important that you do something as soon as possible:
If you lose your passport, you should contact the embassy without delay.

[TahlilGaran] English Thesaurus ▲

at once
1.
immediately.
They were told to leave the building at once.

2.
at the same time.
Everything happened at once, so I didn't have time to ask for advice.

[TahlilGaran] English Idioms Dictionary ▲

at once
immediately
The police came at once when we called them.

[TahlilGaran] English Idioms Dictionary ▲

at once
adv. phr.
1. Without delay; right now or right then; immediately.
Put a burning match next to a piece of paper and it will begin burning at once.
Mother called the children to lunch, and Paul came at once, but Brenda stayed in the sand pile a little longer.
Synonym: RIGHT AWAY or RIGHT OFF.
Compare: ALL AT ONCE².

[TahlilGaran] English Idioms Dictionary ▲