Lipin is a relatively uncommon word, and as such, there are not many synonyms that come to mind. However, the word can be broken down into two parts: "lip" and "-in." The root word lip refers to the fleshy part of the mouth or a similar structure in animals, while the suffix -in is often used to denote proteins or enzymes. With this in mind, possible synonyms could include words that are related to lips or enzymes, such as "labium," "labellum," "protease," or "peptidase." It may require some creative thinking to come up with appropriate synonyms, but these options could suffice in certain contexts.