chain of mountains vs Pamir Mountains

chain of mountains and Pamir Mountains both are nouns.

Word	Noun	Adjective	Verb	Adverb
chain of mountains	Yes	No	No	No
Pamir Mountains	Yes	No	No	No

chain of mountains (noun)	Pamir Mountains (noun)
a series of hills or mountains	a mountain range in central Asia that is centered in Tajikistan but extends into Kyrgyzstan and Afghanistan and Pakistan and western China