LOL, yes my DS5 did that around 3 or 4 too. He always had a great vocabulary as well. He would say something and then I would be quite confused and then he would tell me the made up definition as if I should know it. And then he started to make up expressions...of course they were not at all expressions and were quite comical. He would say "sometimes people say that" I would laugh to myself as clearly he was the only one that would ever say that. DS5 was also interested in other languages and learning them. You may want to try that with your 4yo. My DS enjoyed learning the alphabet in sign language and in spanish and then other words in spanish. He still likes to pick out words and learn them in as many languages as possible.
