The expression "more nether" typically refers to something that is lower or further down, whether in a literal or figurative sense. Some possible synonyms for this phrase could include "lower still," "deeper down," "further below," "beneath even that," or "more deeply nested." Depending on the context, other options might include "subterranean," "underground," "bottommost," "submerged," or "lowest." Ultimately, the most appropriate synonym will depend on the specific meaning and usage of the phrase in question, as well as the writer or speaker's intended emphasis and tone.