Source : Webster's Revised Unabridged Dictionary (1913)

Sidereal \Si*de"re*al\, a. [L. sidereus, from sidus, sideris, a
   constellation, a star. Cf. {Sideral}, {Consider}, {Desire}.]
   1. Relating to the stars; starry; astral; as, sidereal
      astronomy.

   2. (Astron.) Measuring by the apparent motion of the stars;
      designated, marked out, or accompanied, by a return to the
      same position in respect to the stars; as, the sidereal
      revolution of a planet; a sidereal day.

   {Sidereal clock}, {day}, {month}, {year}. See under {Clock},
      {Day}, etc.

   {Sideral time}, time as reckoned by sideral days, or, taking
      the sidereal day as the unit, the time elapsed since a
      transit of the vernal equinox, reckoned in parts of a
      sidereal day. This is, strictly, apparent sidereal time,
      mean sidereal time being reckoned from the transit, not of
      the true, but of the mean, equinoctial point.

Clock \Clock\, n. [AS. clucge bell; akin to D. klok clock, bell,
   G. glocke, Dan. klokke, Sw. klocka, Icel. klukka bell, LL.
   clocca, cloca (whence F. cloche); al perh. of Celtic origin;
   cf. Ir. & Gael. clog bell, clock, W. cloch bell. Cf.
   {Cloak}.]
   1. A machine for measuring time, indicating the hour and
      other divisions by means of hands moving on a dial plate.
      Its works are moved by a weight or a spring, and it is
      often so constructed as to tell the hour by the stroke of
      a hammer on a bell. It is not adapted, like the watch, to
      be carried on the person.

   2. A watch, esp. one that strikes. [Obs.] --Walton.

   3. The striking of a clock. [Obs.] --Dryden.

   4. A figure or figured work on the ankle or side of a
      stocking. --Swift.

   Note: The phrases what o'clock? it is nine o'clock, etc., are
         contracted from what of the clock? it is nine of the
         clock, etc.

   {Alarm clock}. See under {Alarm}.

   {Astronomical clock}.
      (a) A clock of superior construction, with a compensating
          pendulum, etc., to measure time with great accuracy,
          for use in astronomical observatories; -- called a
          regulator when used by watchmakers as a standard for
          regulating timepieces.
      (b) A clock with mechanism for indicating certain
          astronomical phenomena, as the phases of the moon,
          position of the sun in the ecliptic, equation of time,
          etc.

   {Electric clock}.
      (a) A clock moved or regulated by electricity or
          electro-magnetism.
      (b) A clock connected with an electro-magnetic recording
          apparatus.

   {Ship's clock} (Naut.), a clock arranged to strike from one
      to eight strokes, at half hourly intervals, marking the
      divisions of the ship's watches.

   {Sidereal clock}, an astronomical clock regulated to keep
      sidereal time.