Idioms with ONCE

at once
immediately; without delay
We must leave at once.

all at once
simultaneously; at the same time
I can’t do everything all at once.

once or twice
a few times
I’ve only met him once or twice.

once in a while
Everybody makes a mistake once in a while.

once and for all
now and for the last time
We need to settle this matter once and for all.