D defs.my
Entry 2 senses Webster, 1913

Nadir

/(nā"dẽr)/ · Na·dir · IPA /ˈneɪˌdɪɚ/
01 n. That point of the heavens, or lower hemisphere, directly opposite the zenith; the inferior pole of the horizon; the point of the celestial …
  1. 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. 2.
    The lowest point; the time of greatest depression.
    “The seventh century is the nadir of the human mind in Europe.” Hallam.
Phrases & compounds
Nadir of the sun — the axis of the conical shadow projected by the earth.