Saint Nicholas vs Santa

Saint Nicholas and Santa both are nouns.

Word	Noun	Adjective	Verb	Adverb
Saint Nicholas	Yes	No	No	No
Santa	Yes	No	No	No

As nouns, Saint Nicholas and Santa are synonyms defined as:

Saint Nicholas and Santa: the legendary patron saint of children; an imaginary being who is thought to bring presents to children at Christmas

Other synonyms of Saint Nicholas include Father Christmas, Kriss Kringle, Saint Nick, Santa Claus, St. Nick.

Saint Nicholas (noun)	Santa (noun)
a bishop in Asia Minor who is associated with Santa Claus (4th century)	the legendary patron saint of children; an imaginary being who is thought to bring presents to children at Christmas
the legendary patron saint of children; an imaginary being who is thought to bring presents to children at Christmas