Zenith

Webster's Dictionary

(1): ( n.) hence, figuratively, the point of culmination; the greatest height; the height of success or prosperity.

(2): ( n.) That point in the visible celestial hemisphere which is vertical to the spectator; the point of the heavens directly overhead; - opposed to nadir.

The Nuttall Encyclopedia

Name of Arab origin given to the point of the heaven directly overhead, being as it were the pole of the horizon, the opposite point directly under foot being called the Nadir, a word of similar origin; the imaginary line connecting the two passes through the centre of the earth.