Once in fixed expressions

The adverb once is a simple word, but it can have different meanings depending on how it's used in an expression. In this lesson, we'll learn some common expressions where 'once' plays a key role.

At once

immediately or without delay:

• When the fire alarm rang, everyone evacuated the building at once.

All at once

suddenly or at the same time:

• The storm hit the town all at once.
• The students raised their hands all at once.

Once upon a time

used at the beginning of traditional stories to mean a long time ago or in the past:

• Once upon a time, there was a brave knight who fought dragons.

Once in a blue moon

very rarely, almost never

• I see my cousin once in a blue moon because he lives far away.

Once in a while

sometimes, but not very often:

• Step out of your comfort zone once in a while.

Once or twice

a few times:

• I wrote to him once or twice to ask for his advice.

Once and for all

completely or finally:

• We need to put an end to this once and for all.