Lethe vs River Lethe

Lethe and River Lethe both are nouns.

Word	Noun	Adjective	Verb	Adverb
Lethe	Yes	No	No	No
River Lethe	Yes	No	No	No

As nouns, Lethe and River Lethe are synonyms defined as:

Lethe and River Lethe: (Greek mythology) a river in Hades; the souls of the dead had to drink from it, which made them forget all they had done and suffered when they were alive

Lethe (noun)	River Lethe (noun)
(Greek mythology) a river in Hades; the souls of the dead had to drink from it, which made them forget all they had done and suffered when they were alive	(Greek mythology) a river in Hades; the souls of the dead had to drink from it, which made them forget all they had done and suffered when they were alive