Saint Martin vs St. Martin

Saint Martin and St. Martin both are nouns.

Word	Noun	Adjective	Verb	Adverb
Saint Martin	Yes	No	No	No
St. Martin	Yes	No	No	No

As nouns, Saint Martin and St. Martin are synonyms defined as:

Saint Martin and St. Martin: an island in the western Leeward Islands; administered jointly by France and the Netherlands

Other synonyms of Saint Martin include Saint Maarten, Sint Maarten, St. Maarten.

Saint Martin (noun)	St. Martin (noun)
an island in the western Leeward Islands; administered jointly by France and the Netherlands	an island in the western Leeward Islands; administered jointly by France and the Netherlands
	French bishop who is a patron saint of France (died in 397)