Once I got on the train, I felt relieved.

I will do it at once.

Let's try once again.

Let's try it once more.

I gave the document a quick once-over before submitting it.

I like to go hiking once in a while.

Let's settle this once and for all.

They all arrived at once.

I go to the beach once in a blue moon.

This is a once in a lifetime opportunity to travel the world.