1. [n]  a timepiece that shows the time of day
2. [v]  measure the time or duration of an event or action or the person who performs an action in a certain period of time; "he clocked the runners"

1. \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.
   

2. \Clock\ (kl[o^]k), v. t.
   To ornament with figured work, as the side of a stocking.
   

3. \Clock\, v. t. & i.
   To call, as a hen. See {Cluck}. [R.]
   

4. \Clock\, n. (Zo["o]l.)
   A large beetle, esp. the European dung beetle ({Scarab[ae]us
   stercorarius}).
   

A processor's clock or one cycle thereof. The relative execution times of instructions on a computer are usually measured by number of clock cycles rather than seconds. One good reason for this is that clock rates for various models of the computer may increase as technology improves, and it is usually the relative times one is interested in when discussing the instruction set.