netherworld vs fictitious place

netherworld and fictitious place both are nouns.

Word	Noun	Adjective	Verb	Adverb
netherworld	Yes	No	No	No
fictitious place	Yes	No	No	No

As nouns, fictitious place is a hypernym of netherworld; that is, fictitious place is a word with a broader meaning than netherworld:

netherworld: (religion) the world of the dead
fictitious place: a place that exists only in imagination; a place said to exist in fictional or religious writings

Other hypernyms of netherworld include imaginary place, mythical place.

netherworld (noun)	fictitious place (noun)
(religion) the world of the dead	a place that exists only in imagination; a place said to exist in fictional or religious writings