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.
      [1913 Webster]

            Arming to answer in a night alarm.    --Shak.
      [1913 Webster]

   2. Any sound or information intended to give notice of
      approaching danger; a warning sound to arouse attention; a
      warning of danger.
      [1913 Webster]

            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.
      [1913 Webster]

   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.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Alarm \A*larm"\, v. t. [imp. & p. p. Alarmed; p. pr. & vb. n.
   Alarming.] [Alarm, n. Cf. F. alarmer.]
   1. To call to arms for defense; to give notice to (any one)
      of approaching danger; to rouse to vigilance and action;
      to put on the alert.
      [1913 Webster]

   2. To keep in excitement; to disturb.
      [1913 Webster]

   3. To surprise with apprehension of danger; to fill with
      anxiety in regard to threatening evil; to excite with
      sudden fear.
      [1913 Webster]

            Alarmed by rumors of military preparation.
                                                  --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

alarm
    n 1: fear resulting from the awareness of danger [syn: alarm,
         dismay, consternation]
    2: a device that signals the occurrence of some undesirable
       event [syn: alarm, warning device, alarm system]
    3: an automatic signal (usually a sound) warning of danger [syn:
       alarm, alert, warning signal, alarum]
    4: a clock that wakes a sleeper at some preset time [syn: alarm
       clock, alarm]
    v 1: fill with apprehension or alarm; cause to be unpleasantly
         surprised; "I was horrified at the thought of being late
         for my interview"; "The news of the executions horrified
         us" [syn: dismay, alarm, appal, appall, horrify]
    2: warn or arouse to a sense of danger or call to a state of
       preparedness; "The empty house alarmed him"; "We alerted the
       new neighbors to the high rate of burglaries" [syn: alarm,
       alert]

Moby Thesaurus II by Grady Ward, 1.0:

177 Moby Thesaurus words for "alarm":
   Angelus, Angelus bell, Roman candle, abject fear, admonishment,
   admonition, affright, aid to navigation, alarum, alert, amaze,
   amber light, anxiety, apprehension, arouse, astonish, awe,
   balefire, battle cry, beacon, beacon fire, bell, bell buoy,
   birdcall, blinker, blue funk, blue peter, bugle call, buoy, call,
   caution, caution light, caveat, cold feet, consternation,
   cowardice, cry havoc, cry wolf, curdle the blood, daunt,
   deterrent example, discomfort, dismay, disquiet, distress, disturb,
   dread, example, excitement, fear, final notice, final warning,
   flare, fly storm warnings, fog bell, fog signal, fog whistle,
   foghorn, forewarning, fright, frighten, funk, glance, go light,
   gong, gong buoy, green light, heliograph, high sign, hint, horn,
   horrification, horripilate, horror, international alphabet flag,
   international numeral pennant, kick, last post, leer, lesson,
   make one tremble, marker beacon, monition, moose call, moral,
   nervousness, nod, notice, notification, nudge, object lesson,
   panic, panic fear, parachute flare, phobia, pilot flag, poke,
   police whistle, prenotice, quarantine flag, radio beacon,
   raise apprehensions, rallying cry, rebel yell, red flag, red light,
   reveille, rocket, sailing aid, scare, semaphore, semaphore flag,
   semaphore telegraph, shake, sign, signal, signal beacon,
   signal bell, signal fire, signal flag, signal gong, signal gun,
   signal lamp, signal light, signal mast, signal post, signal rocket,
   signal shot, signal siren, signal tower, siren, sound the alarm,
   sound the tocsin, spar buoy, spook, stagger, stampede, startle,
   stop light, strain, stress, summons, surprise, taps, tension,
   terrify, terror, terrorize, the nod, the wink, threat, tip-off,
   tocsin, touch, traffic light, traffic signal, trepidation,
   trumpet call, ultimatum, uneasiness, unholy dread, unman, unnerve,
   unstring, upset, verbum sapienti, war cry, warn, warning,
   warning piece, watch fire, whistle, white flag, wigwag,
   wigwag flag, wink, yellow flag



Easton's 1897 Bible Dictionary:

Alarm
   a particular quivering sound of the silver trumpets to give
   warning to the Hebrews on their journey through the wilderness
   (Num. 10:5, 6), a call to arms, or a war-note (Jer. 4:19; 49:2;
   Zeph. 1:16).