Saint Nicholas vs Saint Nick

Saint Nicholas and Saint Nick both are nouns.

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

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

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

Saint Nicholas (noun)	Saint Nick (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