What is synonym for prairie?
I think a better synonym is plain (extensive area of flat land). A swamp is a wet damp place, prairies or plain are not necessarily wet.
A synonym of a synonym is an alternate word for one of the original word's synonyms: A synonym for "abundance" is "plenty." In that sentence the word "abundance" is the original, and "plenty" is the synonym. It follows that a synonym of the synonym is one of the synonyms for the word, "plenty;" for example, "copiousness."