border vs boundary line

border and boundary line both are nouns.

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

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

Other synonyms of border include borderline, delimitation, mete.

border (noun)	boundary line (noun)
a strip forming the outer edge of something	a line that indicates a boundary
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

border (verb)	boundary line (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