na·dir 
(nādər, -dîr′)
(nādər, -dîr′)n.
1. Astronomy A point on the celestial sphere directly below the observer, diametrically opposite the zenith.
2. The lowest point: the nadir of their fortunes.
[Middle English, from Medieval Latin, from Arabic naẓīr (as-samt), opposite (the zenith), from naẓara, to see, watch; see nr in the Appendix of Semitic roots.]