at once
prep. phr..prep. phr.. to do something immediately or at the same time as something else.
prep. phr.. functioning as an adverbial of time; indicates either instantaneous action or the simultaneous occurrence of multiple events.
Please come to my office at once.
The fire alarm went off and everyone started running for the exits at once.
The conductor signaled the orchestra, and every musician began to play at once, creating a sudden wall of sound.
From Middle English at ones, equivalent to at + once.
usually placed at the end of a clause or after the verb.
distinguish between the 'immediately' sense and the 'simultaneously' sense by looking at whether the subject is performing one action or many people are acting together.
He did it at one.He did it at once.the word 'once' is a fixed part of this phrase and cannot be replaced by the number 'one'.