This is truly a once in a lifetime opportunity.

He drew a hendecagon shape.

We go on a family trip once a year.

His party trick is perfect for livening up the party.

He continued to write that report all night.

My birthday is on the thirty-first.

My father is forty-one years old.

He is known as a one-hit wonder singer.

Nitrogen monoxide is a cause of air pollution.

The First International was an international organization of workers.