Synonyms of once in English:

once


See US English definition of once

See UK English definition of once

adverb

1‘I saw him only once’

SYNONYMS
on one occasion, one time, one single time
ANTONYMS

twice, many times

2‘he did not once help’

SYNONYMS
ever, at any time, on any occasion, at all, under any circumstances, on any account, in a million years

3‘they were friends once’

SYNONYMS
formerly, previously, in the past, at one time, at one point, once upon a time, on a former occasion, on one occasion, one time, in one case, time was when, in days gone by, in times gone by, back in the day, in times past, in the old days, in the good old days, long ago
archaic sometime, erst, erstwhile, whilom
literary in days of yore, in times of yore, of yore
ANTONYMS

now


conjunction

1‘he'll be all right once she's gone’

SYNONYMS
as soon as, when, after, immediately after, the instant, the minute, the moment, the second
British informal immediately

Phrases

    once in a while

    ‘once in a while a car went past’


    SYNONYMS
    occasionally, from time to time, now and again, now and then, every now and again, every now and then, every so often, every once in a while, on occasion, on occasions, on the odd occasion, at times, sometimes, off and on, at intervals, periodically, sporadically, spasmodically, erratically, irregularly, intermittently, by fits and starts, in fits and starts, fitfully, discontinuously, piecemeal
    rare interruptedly
    once and for all

    1‘you must decide once and for all’


    SYNONYMS
    conclusively, decisively, finally, positively, absolutely, determinedly, definitely, definitively, irrevocably

    2‘he has gone once and for all’


    SYNONYMS
    for good, for always, forever, permanently, finally, in perpetuity
    informal for keeps
    at once

    1‘you must leave at once’


    SYNONYMS
    immediately, right away, right now, this instant, this minute, this moment, this second, now, straight away, instantly, instantaneously, directly, suddenly, abruptly, summarily, forthwith, promptly, without delay, without hesitation, without further ado
    quickly, as fast as possible, as soon as possible, fast, speedily, with all speed
    informal like a shot, in a flash, like a flash, before you can say Jack Robinson, in two shakes, in two shakes of a lamb's tail
    ANTONYMS

    later, in due course

    2‘all the guests arrived at once’


    SYNONYMS
    at the same time, at one and the same time, at the same instant, at the same moment, together, all together, simultaneously
    as a group, in unison, in concert, in chorus
    ANTONYMS

    singly, in dribs and drabs