niezamężna in English:

an unwed teenage mother

Tom is unmarried.

I'm a thirty-year-old unmarried woman.

As far as I know, she's still unmarried.

They are both unmarried.

He is unmarried and has no brothers or sisters.

I'm glad to hear that she is unmarried.

Tom's older daughter is still unmarried.

My aunt is unmarried.

She remained unmarried until death.

Although an increase of unmarried mothers is needed in order to escape the declining birth rate for some reason public opinion in Japan is avoiding this argument.

The experiment was made on a hundred unmarried males.

My brother, being yet unmarried, did not keep house, but boarded himself and his apprentices in another family.

For a start, he was the illegitimate son of an unmarried mother.

The book's weak-point is that it lacks credibility when a married writer recommends remaining unmarried.