boundary line vs border

boundary line and border both are nouns.

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

As nouns, boundary line and border are synonyms defined as:

Other synonyms of boundary line include borderline, delimitation, mete.

boundary line (noun)	border (noun)
a line that indicates a boundary	a strip forming the outer edge of something
	a decorative recessed or relieved surface on an edge
	a line that indicates a boundary
	the boundary of a surface
	the boundary line or the area immediately inside the boundary

boundary line (verb)	border (verb)
	lie adjacent to another or share a boundary
	extend on all sides of simultaneously; encircle
	enclose in or as if in a frame
	provide with a border or edge
	form the boundary of; be contiguous to