royal line vs royalty

royal line and royalty both are nouns.

Word	Noun	Adjective	Verb	Adverb
royal line	Yes	No	No	No
royalty	Yes	No	No	No

As nouns, royal line and royalty are synonyms defined as:

Other synonyms of royal line include royal family, royal house.

royal line (noun)	royalty (noun)
royal persons collectively	royal persons collectively
	payment to the holder of a patent or copyright or resource for the right to use their property