Bathybic is a term that refers to the deep oceanic zone. Although there aren't many direct synonyms for this word, there are a few related terms that can be used interchangeably. For instance, "abyssal" refers to the deepest part of the ocean, while "pelagic" is used to describe marine life that dwells in open water. "Hadopelagic" and "demersal" are other words that might be used to describe organisms that live in the deep ocean. Additionally, the term "benthic" is often used to describe the organisms that live on the seafloor. While these terms may not be precise synonyms for "bathybic," they can be helpful when describing the deep ocean and the life that inhabits it.