Gemellus is a Latin word that means "twin" or "double." It is often used in anatomical terms to describe muscles or ligaments that come in pairs. Some synonyms for gemellus include duplicate, dual, twofold, paired, coupled, and matched. Other related words might include identical, twinned, mirrored, and symmetrical. In a broader sense, the concept of "twins" or "doubles" could also be expressed through words like doppelganger, clone, replica, or mirror image. Whether you are referring to physical structures or more metaphorical concepts, there are many ways to convey the idea of something that comes in a pair or has an identical counterpart.