Foster mother and Surrogate mother

Foster mother noun - A woman who is a foster parent and raises another's child.

Surrogate mother and foster mother are semantically related. In some cases you can use "Surrogate mother" instead a noun phrase "Foster mother".

Surrogate mother noun - A woman who bears a child for a couple where the wife is unable to do so.

Foster mother and surrogate mother are semantically related. You can use "Foster mother" instead a noun phrase "Surrogate mother".