Saint Mark vs St. Mark

Saint Mark and St. Mark both are nouns.

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

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

Saint Mark and St. Mark: Apostle and companion of Saint Peter; assumed to be the author of the second Gospel

Other synonyms of Saint Mark include Mark, Mark the Evangelist.

Saint Mark (noun)	St. Mark (noun)
Apostle and companion of Saint Peter; assumed to be the author of the second Gospel	Apostle and companion of Saint Peter; assumed to be the author of the second Gospel