oubliette vs dungeon

oubliette and dungeon both are nouns.

Word	Noun	Adjective	Verb	Adverb
oubliette	Yes	No	No	No
dungeon	Yes	No	No	No

As nouns, dungeon is a hypernym of oubliette; that is, dungeon is a word with a broader meaning than oubliette:

oubliette: a dungeon with the only entrance or exit being a trap door in the ceiling
dungeon: a dark cell (usually underground) where prisoners can be confined

oubliette (noun)	dungeon (noun)
a dungeon with the only entrance or exit being a trap door in the ceiling	the main tower within the walls of a medieval castle or fortress
	a dark cell (usually underground) where prisoners can be confined