nadir
Concise Oxford English Dictionary © 2008 Oxford University Press:
nadir /ˈneɪdɪə, ˈnadɪə/
▶noun
- 1 the lowest or most unsuccessful point: his fortunes reached their nadir.
- 2 Astronomy the point on the celestial sphere directly below an observer. The opposite of zenith.
– origin ME: via Fr. from Arab. naẓīr (as-samt) ‘opposite (to the zenith)’.
'nadir' also found in these Oxford entries:

