Rainier vs Mount Rainier

Rainier and Mount Rainier both are nouns.

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

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

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

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

Rainier (noun)	Mount 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)