Nadir

[ney-der, ney-deer] /ˈneɪ dər, ˈneɪ dɪər/

noun
1.
Astronomy. the point on the celestial sphere directly beneath a given position or observer and diametrically opposite the zenith.
2.
Astrology. the point of a horoscope opposite the midheaven: the cusp of the fourth house.
3.
the lowest point; point of greatest adversity or despair.
/ˈneɪdɪə; ˈnæ-/
noun
1.
the point on the celestial sphere directly below an observer and diametrically opposite the zenith
2.
the lowest or deepest point; depths: the nadir of despair
n.

late 14c., in astronomical sense, from Medieval Latin nadir, from Arabic nazir “opposite to,” in nazir as-samt, literally “opposite of the zenith,” from nazir “opposite” + as-samt “zenith” (see zenith). Transferred sense of “lowest point (of anything)” is first recorded 1793.
nadir
(nā’dər)
The point on the celestial sphere that is directly below the observer (90 degrees below the celestial horizon). Compare zenith.