followtheyellowbrickroad I enjoy your questions, and I am detecting a real interest in linguistics, which can be studied as a branch of psychology (we’re also interested in how the brain deals with language). You should think about studying one of these topics at Uni, or perhaps you’re just messing about.
To answer I don’t think there is a synonym for synonym. I have a program on my computer (which I recommend but you have to pay for the full version) called “visual thesaurus”. It links in to a big database of word meanings and there relationships. When I typed in synonym it came up with “equivalent word”, and I don’t think that counts.