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
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