Mount Rainier vs Mt. Rainier

Mount Rainier and Mt. Rainier both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mount Rainier	Yes	No	No	No
Mt. Rainier	Yes	No	No	No

As nouns, Mount Rainier and Mt. Rainier are synonyms defined as:

Mount Rainier and Mt. Rainier: a mountain peak in central Washington; highest peak in the Cascade Range; (14,410 feet high)

Other synonyms of Mount Rainier include Mount Tacoma, Rainier.

Mount Rainier (noun)	Mt. Rainier (noun)
a mountain peak in central Washington; highest peak in the Cascade Range; (14,410 feet high)	a mountain peak in central Washington; highest peak in the Cascade Range; (14,410 feet high)