good manners vs courtesy

good manners and courtesy both are nouns.

Word	Noun	Adjective	Verb	Adverb
good manners	Yes	No	No	No
courtesy	Yes	No	No	No

As nouns, good manners and courtesy are synonyms defined as:

good manners (noun)	courtesy (noun)
a courteous manner	a courteous or respectful or considerate act
	a courteous manner
	a courteous or respectful or considerate remark