lower world—
1. mortal earth as opposed to heaven:
- Innumerable high-dressed gentlemen, gods of this lower world, are gone all to inorganic powder.
2. the realm of the dead:
- In the mysteries of Eleusis, the return of Cora from the lower world was regarded as the symbol of immortality.
underworld—
1. the community of criminals:
- He was known in the underworld circles as a luxury loan shark, lending money to casino gamblers.
2. = lower world 2:
- Auernus was the name of a deep lake near Puteoli, the reputed entrance to the underworld.
Note: The compound does not correlate in meaning with the phrase down under world—(coll.) Australia or New Zealand:
- Things have been busy in the down under world I have been in recently. I have flown back and forward between Australia and New Zealand…