Thurs Sotah 24

The Mishna says (according to rabanan) that you don't brings as a Sotah a wife "whose not fit to give birth." Rashi explains it refers to a woman who drank a potion that makes her barren.

Tosfos asks: this cannot be the definition, since in Kesuvos a Braisa lists "a woman who's not fit to give birth" with a woman who becomes barren. So they seem to be different people.

Tosfos answers: we refer to a woman that didn't marry until forty years old. Alternatively, a woman that didn't get married again after her first husband and didn't plan to either. The gemara says that in either case, she can no longer have children.