Dark Ages vs Middle Ages

Dark Ages and Middle Ages both are nouns.

Word	Noun	Adjective	Verb	Adverb
Dark Ages	Yes	No	No	No
Middle Ages	Yes	No	No	No

As nouns, Dark Ages and Middle Ages are synonyms defined as:

Dark Ages and Middle Ages: the period of history between classical antiquity and the Italian Renaissance

Dark Ages (noun)	Middle Ages (noun)
the period of history between classical antiquity and the Italian Renaissance	the period of history between classical antiquity and the Italian Renaissance