At once
At once adverb - Without delay or hesitation; with no time intervening.
Once only
Mutual synonyms
Cite this Source
Once only and At once. (2016). Retrieved 2026, July 29, from https://thesaurus.plus/related/at_once/once_only
At once & Once only. N.p., 2016. Web. 29 Jul. 2026. <https://thesaurus.plus/related/at_once/once_only>.
Once only or At once. 2016. Accessed July 29, 2026. https://thesaurus.plus/related/at_once/once_only.
Google Ngram Viewer shows how "at once" and "once only" have occurred on timeline