Nadir (nād&etilde_;r), n. [F., Sp., & It. nadir; all fr. Ar. nazīru's samt nadir, prop., the point opposite the zenith (as samt), in which nazīr means alike, corresponding to. Cf. Azimuth, Zenith.] 1. That point of the heavens, or lower hemisphere, directly opposite the zenith; the inferior pole of the horizon; the point of the celestial sphere directly under the place where we stand.[1913 Webster]
2. The lowest point; the time of greatest depression.[1913 Webster]
The seventh century is the nadir of the human mind in Europe.
Nadir of the sun (Astron.), the axis of the conical shadow projected by the earth. Crabb.[1913 Webster]