Star-Spangled Banner vs American flag

Star-Spangled Banner and American flag both are nouns.

Word	Noun	Adjective	Verb	Adverb
Star-Spangled Banner	Yes	No	No	No
American flag	Yes	No	No	No

As nouns, Star-Spangled Banner and American flag are synonyms defined as:

Star-Spangled Banner and American flag: the national flag of the United States of America

Other synonyms of Star-Spangled Banner include Old Glory, Stars and Stripes.

Star-Spangled Banner (noun)	American flag (noun)
the national flag of the United States of America	the national flag of the United States of America