Foster father and Father surrogate

Foster father noun - A man who is a foster parent.

Father surrogate and foster father are semantically related. In some cases you can use "Father surrogate" instead a noun phrase "Foster father".

Father surrogate noun - A man who takes over all the functions of the real father.

Foster father and father surrogate are semantically related. Sometimes you can replace phrase "Foster father" with "Father surrogate", this phrases are similar.