voi khat; e.g. Once is enough = Voi khat cu a za ko.
all at once = 1. a dihlak in voi khat ah; e.g. They came all at once = An dihlak in voi khat ah an ra; 2. khulrang tein; e.g. He turned off the lights and all at once it was dark = Mei kha a hmih i chikkhatte ah a mui dup ko.
at once = Khulrang tein ra tuah.