Protosyntax is a term used to describe the ways in which syntax developed in early human languages. Although there are not many direct synonyms for this specific word, there are a few terms that could be used in its place, depending on the context of the sentence. For example, the term "early syntax" could be used to refer to the same idea. Alternatively, one could use terms like "primitive syntax," "rudimentary syntax," or "basic syntax" to describe the early stages of language development. Overall, while there may not be many direct synonyms for protosyntax, there are many ways to describe similar concepts using related terms.