Definitions
There are 2 meanings of the phrase
At Once.
At Once - as an adverb
Without delay or hesitation; with no time intervening
Example: "He answered immediately"
Synonyms (Exact Relations)
directlyforthwithimmediatelyinstantlylike a shotnowright awaystraight offstraightawaySimultaneously
Example: "He took three cookies at a time"
Synonyms (Exact Relations)
at a timeat one timeExample Sentences
"He decided to leave the room at once."
"Please complete the task at once."
"The machine stopped working at once."
"She turned on the lights at once."
"The alarm went off, and everyone evacuated at once."