Mt. Rainier vs Rainier

Mt. Rainier and Rainier both are nouns.

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

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

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

Other synonyms of Mt. Rainier include Mount Rainier, Mount Tacoma.

Mt. Rainier (noun)	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)