Synonyms of at once

Adverb

1. immediately, instantly, straightaway, straight off, directly, now, right away, at once, forthwith, like a shot

usage: without delay or hesitation; with no time intervening; "he answered immediately"; "found an answer straightaway"; "an official accused of dishonesty should be suspended forthwith"; "Come here now!"

2. at a time, at once, at one time

usage: simultaneously; "he took three cookies at a time"