boundary line vs boundary

boundary line and boundary both are nouns.

Word	Noun	Adjective	Verb	Adverb
boundary line	Yes	No	No	No
boundary	Yes	No	No	No

As nouns, boundary is a hypernym of boundary line; that is, boundary is a word with a broader meaning than boundary line:

Other hypernyms of boundary line include bound, bounds.

boundary line (noun)	boundary (noun)
a line that indicates a boundary	the greatest possible degree of something
	the line or plane indicating the limit or extent of something
	a line determining the limits of an area