diagonal vs straight line

diagonal and straight line both are nouns.

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

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

diagonal: a line or cut across a fabric that is not at right angles to a side of the fabric
straight line: a line traced by a point traveling in a constant direction; a line of zero curvature

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

diagonal: (geometry) a straight line connecting any two vertices of a polygon that are not adjacent
straight line: a line traced by a point traveling in a constant direction; a line of zero curvature

diagonal (noun)	straight line (noun)
a punctuation mark (/) used to separate related items of information	a line traced by a point traveling in a constant direction; a line of zero curvature
an oblique line of squares of the same color on a checkerboard
(mathematics) a set of entries in a square matrix running diagonally either from the upper left to lower right entry or running from the upper right to lower left entry
a line or cut across a fabric that is not at right angles to a side of the fabric
(geometry) a straight line connecting any two vertices of a polygon that are not adjacent

diagonal (adjective)	straight line (adjective)
having an oblique or slanted direction
connecting two nonadjacent corners of a plane figure or any two corners of a solid that are not in the same face