Mile-High City vs Denver

Mile-High City and Denver both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mile-High City	Yes	No	No	No
Denver	Yes	No	No	No

As nouns, Mile-High City and Denver are synonyms defined as:

Mile-High City and Denver: the state capital and largest city of Colorado; located in central Colorado on the South Platte river

Other synonyms of Mile-High City include capital of Colorado.

Mile-High City (noun)	Denver (noun)
the state capital and largest city of Colorado; located in central Colorado on the South Platte river	the state capital and largest city of Colorado; located in central Colorado on the South Platte river