Eternal abyss refers to a never-ending depth or bottomless pit. However, there are various synonyms that can be used to express the same idea. These synonyms include perpetual depth, unfathomable chasm, endless void, infinite cavern, boundless pit, and immeasurable gulf. Each of these words emphasizes the idea of immensity and vastness, conveying the sense of something that is beyond measure or comprehension. Additionally, these synonyms can be used in different contexts to express a similar idea, such as in poetry, literature, and philosophy. Thus, by using these synonyms, writers and poets can convey the idea of an eternal abyss in a more creative and captivating way.