tangent vs straight line

tangent and straight line both are nouns.

Word	Noun	Adjective	Verb	Adverb
tangent	Yes	No	No	No
straight line	Yes	No	No	No

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

tangent: a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point
straight line: a line traced by a point traveling in a constant direction; a line of zero curvature

tangent (noun)	straight line (noun)
ratio of the opposite to the adjacent side of a right-angled triangle	a line traced by a point traveling in a constant direction; a line of zero curvature
a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point