ETYM French, Spanish, and Italian nadir; all from Arabic nasîru's samt nadir, prop., the point opposite the zenith (as samt), in which nasîr means alike, corresponding to. Related to Azimuth, Zenith.
1. An extreme state of adversity; the lowest point of anything; SYN. low-water mark.
2. The point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected.
Point opposite zenith; lowest point.
The point on the celestial sphere vertically below the observer and hence diametrically opposite the zenith. The term is used metaphorically to mean the low point of a person’s fortunes.