Synonyms for Once:

adv.

in the past; occurred one time only (adverb)
already, earlier, before, once only, one, previously.

n.

beyond, after, Since, subsequently, following, in the course of time, in time, ensuing, succeeding, subsequent. ago, uniquely, once only, one day. earlier, Aforetime, one shot, already, unrepeatable, isolated, before, in/at one fell swoop, precede, Beforetime, once in a lifetime, previously, one-off. formerly (noun)
previously, earlier.
one time (noun)
twice, one.

Other synonyms:

ago, Aforetime, Beforetime. earlier, previously, one-off, already, unrepeatable. isolated, before. singular
one shot.

Usage examples for once

  1. " His mother made up her mind to, once – The Wide Awake Girls in Winsted by Katharine Ellis Barrett
  2. This didn't seem possible to me, and once I went out with her to see. – The Chief Legatee by Anna Katharine Green
  3. When he does come, tell him I want to see him at once at once do you understand? – Tales of Fantasy and Fact by Brander Matthews