Benthal is a scientific term used to describe the bottom layer of a body of water, whether it be a lake, river, or ocean. While there are no exact synonyms for this word, there are related terms that can be used to describe the same concept. For example, the benthic zone refers to the entire bottom layer of a body of water, including both the sediment and the organisms that live within it. Other terms, such as the littoral zone, pelagic zone, and abyssal zone, describe different areas of the water column. Overall, while there may not be an exact synonym for benthal, there are many related terms in the field of limnology and oceanography that can be used to describe the same concept.