Santa Claus vs St. Nick

Santa Claus and St. Nick both are nouns.

Word	Noun	Adjective	Verb	Adverb
Santa Claus	Yes	No	No	No
St. Nick	Yes	No	No	No

As nouns, Santa Claus and St. Nick are synonyms defined as:

Santa Claus and St. Nick: 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 Nicholas, Saint Nick, Santa.

Santa Claus (noun)	St. Nick (noun)
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