Nadir \Na"dir\, n. [F., Sp., & It. nadir; all fr. Ar. nas[=i]ru's samt nadir, prop., the point opposite the zenith (as samt), in which nas[=i]r 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.

2. The lowest point; the time of greatest depression.

The seventh century is the nadir of the human mind in Europe. --Hallam.

Nadir of the sun (Astron.), the axis of the conical shadow projected by the earth. --Crabb.

Source: Webster's Revised Unabridged Dictionary (1913)