What is "diagonial"

Diagonial \Di`a*go"ni*al\, a. Diagonal; diametrical; hence; diametrically opposed. [Obs.]

Sin can have no tenure by law at all, but is rather an eternal outlaw, and in hostility with law past all atonement; both diagonal contraries, as much allowing one another as day and night together in one hemisphere.
--Milton.

a. 1 (obsolete form of diagonal English) 2 (context obsolete English) diametrically opposed