Synonyms for once

modified

1. One time

   this time, but once, once only, one time before, already, one, just this once, for the nonce, not more than once, never again, a single time, one time previously, on one occasion, only one time.

   Antonyms twice*, many times, frequently.

2. Formerly

   long ago, previously, earlier; see formerly.

at once

1. Immediately

   now, quickly, this moment; see immediately.

2. Simultaneously

   all at once, at the same time, concurrently; see together 2.

for once