Geryon vs mythical monster

Geryon and mythical monster both are nouns.

Word	Noun	Adjective	Verb	Adverb
Geryon	Yes	No	No	No
mythical monster	Yes	No	No	No

As nouns, mythical monster is a hypernym of Geryon; that is, mythical monster is a word with a broader meaning than Geryon:

Geryon: (Greek mythology) a mythical monster with three heads that was slain by Hercules
mythical monster: a monster renowned in folklore and myth

Other hypernyms of Geryon include mythical creature.

Geryon (noun)	mythical monster (noun)
(Greek mythology) a mythical monster with three heads that was slain by Hercules	a monster renowned in folklore and myth