1.That point in the visible celestial hemisphere which is vertical to the spectator; the point of the heavens directly overhead; opposed to nadir. "From morn To noon he fell, from noon to dewy eve, A summer's day; and with the setting sun Dropped from the zenith, like a falling star."
2.Hence, figuratively, the point of culmination; the greatest height; the height of success or prosperity. "I find my zenith doth depend upon A most auspicious star." "This dead of midnight is the noon of thought, And wisdom mounts her zenith with the stars." "It was during those civil troubles... this aspiring family reached the zenith."