At the same time, as in We can't all fit into the boat at once. [First half of 1200s] Also see at one time, def. 1.
Immediately, as in Mother told the children to come inside at once. [First half of 1500s]
Words nearby at once
How to use at once in a sentence
Fryberg left behind a dense record all-at-once ordinary and disturbing, that leaves more questions than answers.The Homecoming Prince Who Tweeted His Killing Spree|Brandy Zadrozny|October 24, 2014|DAILY BEAST
The localisation of sensibility was merging into a unified perception whereby people would presently know all-over and at-once.
Then the flagship hauled home every rope by the silent ‘all-at-once’ action of one hundred men.An Orkney Maid|Amelia Edith Huddleston Barr
Then we perceived there were two fires throwing up their smoke in the morning sun—the "Come-at-once" signal.Through the Heart of Patagonia|H. Hesketh Prichard
All at-once the enraged chief showed by his gestures that he had resolved what course he would take.Typee|Herman Melville
And Joan, somehow or other, was aware of this, for she saw things all-at-once and all-over.