straight line vs secant

straight line and secant both are nouns.

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

As nouns, secant is a hyponym of straight line; that is, secant is a word with a more specific, narrower meaning than straight line:

straight line: a line traced by a point traveling in a constant direction; a line of zero curvature
secant: a straight line that intersects a curve at two or more points

Other hyponyms of straight line include perpendicular, asymptote, tangent, radius, diameter, chord, element, bias, diagonal, diagonal, vector.

straight line (noun)	secant (noun)
a line traced by a point traveling in a constant direction; a line of zero curvature	ratio of the hypotenuse to the adjacent side of a right-angled triangle
	a straight line that intersects a curve at two or more points