The opposite of nadir, it's from the Arabic for "road above"
[DOC] [TLE] Le Zenith - definition of Le Zenith by The Free Dictionary [PAR] nadir - Zenith derived from Arabic samt ar-ras, "the way or road above one's ... 
Noun, 1. zenith - the point above the observer that is directly opposite the nadir 
on the ... apex, high noon, apogee, acme, vertex His career is now at its zenith.