noun
Etymology: cardinal (I)
1.
a. : one of the four principal points of the compass north, south, east, and west
b. in magical ritual : one of the four principal directional points of the compass or one of the additional points zenith, nadir, and center
2. of a lens or lens system : one of the two principal foci, the two principal points, or the two nodal points — called also Gauss point