Santa Claus vs Saint Nicholas

Santa Claus and Saint Nicholas both are nouns.

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

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

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

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

Santa Claus (noun)	Saint Nicholas (noun)
the legendary patron saint of children; an imaginary being who is thought to bring presents to children at Christmas	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