Source : Webster's Revised Unabridged Dictionary (1913)

Zenith \Ze"nith\ (?; 277), n. [OE. senyth, OF. cenith, F.
   z['e]nith, Sp. zenit, cenit, abbrev. fr. Ar. samt-urras way
   of the head, vertical place; samt way, path + al the + ras
   head. Cf. {Azimuth}.]
   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.      --Milton.

   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.                                 --Shak.

            This dead of midnight is the noon of thought, And
            wisdom mounts her zenith with the stars. --Mrs.
                                                  Barbauld.

            It was during those civil troubles . . . this
            aspiring family reached the zenith.   --Macaulay.

   {Zenith distance}. (Astron.) See under {Distance}.

   {Zenith sector}. (Astron.) See {Sector}, 3.

   {Zenith telescope} (Geodesy), a telescope specially designed
      for determining the latitude by means of any two stars
      which pass the meridian about the same time, and at nearly
      equal distances from the zenith, but on opposite sides of
      it. It turns both on a vertical and a horizontal axis, is
      provided with a graduated vertical semicircle, and a level
      for setting it to a given zenith distance, and with a
      micrometer for measuring the difference of the zenith
      distances of the two stars.