1. (adverb)immediately, instantly, straightaway, straight off, directly, now, right away, at once, forthwith, like a shot without delay or hesitation; with no time intervening Synonyms: now, at one time, straight, at present, like a shot, instantly, instantaneously, in a flash, at once, outright, nowadays, at a time, today, direct, directly, forthwith, promptly, straight off, straightaway, right away, flat, immediately
2. (adverb)at a time, at once, at one time simultaneously Synonyms: at once, straightaway, like a shot, now, at one time, straight off, formerly, at a time, directly, immediately, right away, instantly, once, erstwhile, erst, forthwith
Synonyms, Thesaurus & Antonyms of 'at once'
English Synonyms and Antonyms
1. at once The strong and general human tendency to procrastination is shown in the progressive weakening of the various words in this group. Immediately primarily signifies without the intervention of anythi Synonyms: immediately, at once, instanter, presently, straightway, directly, instantly, right away, this instant, forthwith, now, right off, without delay Antonyms: after a while, by and by, hereafter, in the future, some time
Synonyms for at once 
