Once1. (adv.) By limitation to the number one; for one time; not twice nor any number of times more than one.
2. (adv.) At some one period of time; -- used indefinitely.
3. (adv.) At any one time; -- often nearly equivalent to ever, if ever, or whenever; as, once kindled, it may not be quenched.
Thesaurus Entries
alone, already, ancient, anytime, anyway, anywise, apart, at a stroke, at all, at any time, at intervals, at once, at one time, at times, at whatever time, before, by itself, bygone, conclusively, decidedly, definitely, directly, earlier, early, erstwhile, finally, for good, fore, former, formerly, heretofore, if ever, immediately, immemorial, in a jiffy, in a trice, in a wink, in the singular, individually, instantly, just this once, late, long ago, no matter when, now and again, occasionally, old, olden, on one occasion, once for all, one by one, one day, one fine morning, one time, onetime, only once, particularly, past, per se, periodically, positively, prehistoric, previous, previously, primeval, primitive, prior, promptly, quondam, recent, right away, separately, severally, simultaneously, single-handedly, singly, singularly, some time ago, sometime, sometimes, sporadically, then, time was, together, whenever, whensoever, whilom, without delay