The Collaborative International Dictionary of English v.0.48:

Alarm \A*larm"\ ([.a]*l[aum]rm"), n. [F. alarme, It. all' arme
   to arms ! fr. L. arma, pl., arms. See Arms, and cf.
   Alarum.]
   1. A summons to arms, as on the approach of an enemy.
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            Arming to answer in a night alarm.    --Shak.
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   2. Any sound or information intended to give notice of
      approaching danger; a warning sound to arouse attention; a
      warning of danger.
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            Sound an alarm in my holy mountain.   --Joel ii. 1.
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   3. A sudden attack; disturbance; broil. [R.] "These home
      alarms." --Shak.
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            Thy palace fill with insults and alarms. --Pope.
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   4. Sudden surprise with fear or terror excited by
      apprehension of danger; in the military use, commonly,
      sudden apprehension of being attacked by surprise.
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            Alarm and resentment spread throughout the camp.
                                                  --Macaulay.
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   5. A mechanical contrivance for awaking persons from sleep,
      or rousing their attention; an alarum.
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   Alarm bell, a bell that gives notice on danger.

   Alarm clock or watch, a clock or watch which can be so
      set as to ring or strike loudly at a prearranged hour, to
      wake from sleep, or excite attention.

   Alarm gauge, a contrivance attached to a steam boiler for
      showing when the pressure of steam is too high, or the
      water in the boiler too low.

   Alarm post, a place to which troops are to repair in case
      of an alarm.
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   Syn: Fright; affright; terror; trepidation; apprehension;
        consternation; dismay; agitation; disquiet; disquietude.

   Usage: Alarm, Fright, Terror, Consternation. These
          words express different degrees of fear at the
          approach of danger. Fright is fear suddenly excited,
          producing confusion of the senses, and hence it is
          unreflecting. Alarm is the hurried agitation of
          feeling which springs from a sense of immediate and
          extreme exposure. Terror is agitating and excessive
          fear, which usually benumbs the faculties.
          Consternation is overwhelming fear, and carries a
          notion of powerlessness and amazement. Alarm agitates
          the feelings; terror disorders the understanding and
          affects the will; fright seizes on and confuses the
          sense; consternation takes possession of the soul, and
          subdues its faculties. See Apprehension.
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The Collaborative International Dictionary of English v.0.48:

Clock \Clock\ (kl[o^]k), 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; in ordinary mechanical clocks for
      domestic or office use the time is indicated on a
      typically circular face or dial plate containing two
      hands, pointing to numbers engraved on the periphery of
      the face, thus showing the hours and minutes. The works of
      a mechanical clock 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. In electrical or electronic
      clocks, the time may be indicated, as on a mechanical
      clock, by hands, but may also be indicated by direct
      digital readout, with the hours and minutes in normal
      Arabic numerals. The readout using hands is often called
      analog to distinguish it from the digital readout. Some
      clocks also indicate the seconds. Clocks are not adapted,
      like the watch, to be carried on the person. Specialized
      clocks, such as atomic clocks, may be constructed on
      different principles, and may have a very high precision
      for use in scientific observations.
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   2. A watch, esp. one that strikes. [Obs.] --Walton.
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   3. The striking of a clock. [Obs.] --Dryden.
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   4. A figure or figured work on the ankle or side of a
      stocking. --Swift.
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   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.
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   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.
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WordNet (r) 3.0 (2006):

alarm clock
    n 1: a clock that wakes a sleeper at some preset time [syn:
         alarm clock, alarm]