Cumulostratus is a type of cloud that is typically characterized by a flat base and a distinct, layered appearance. While there are no exact synonyms for the term, there are a few other terms that can be used to describe clouds that share similar characteristics. One possible synonym for cumulostratus is altocumulus, which is a middle-level cloud that often appears in large sheets or layers. Another possible synonym is cirrocumulus, which is a high-level cloud that is often characterized by small, white, fluffy masses. Ultimately, the choice of terminology will depend on the specific appearance and location of the cloud in question, as well as the context in which it is being used.