Hydra vs Lernaean Hydra

Hydra and Lernaean Hydra both are nouns.

Word	Noun	Adjective	Verb	Adverb
Hydra	Yes	No	No	No
Lernaean Hydra	Yes	No	No	No

As nouns, Hydra and Lernaean Hydra are synonyms defined as:

Hydra and Lernaean Hydra: (Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones

Hydra (noun)	Lernaean Hydra (noun)
a long faint constellation in the Southern Hemisphere near the equator stretching between Virgo and Cancer	(Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones
(Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones