The Collaborative International Dictionary of English v.0.48:

Calm \Calm\ (k[aum]m), a. [Compar. Calmer (-[~e]r); superl.
   Calmest (-[e^]st)]
   1. Not stormy; without motion, as of winds or waves; still;
      quiet; serene; undisturbed. "Calm was the day." --Spenser.
      [1913 Webster]

            Now all is calm, and fresh, and still. --Bryant.
      [1913 Webster]

   2. Undisturbed by passion or emotion; not agitated or
      excited; tranquil; quiet in act or speech. "Calm and
      sinless peace." --Milton. "With calm attention." --Pope.
      [1913 Webster]

            Such calm old age as conscience pure
            And self-commanding hearts ensure.    --Keble.

   Syn: Still; quiet; undisturbed; tranquil; peaceful; serene;
        composed; unruffled; sedate; collected; placid.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Calm \Calm\ (k[aum]m), n. [OE. calme, F. calme, fr. It. or Sp.
   calma (cf. Pg. calma heat), prob. fr. LL. cauma heat, fr. Gr.
   kay^ma burning heat, fr. kai`ein to burn; either because
   during a great heat there is generally also a calm, or
   because the hot time of the day obliges us seek for shade and
   quiet; cf. Caustic]
   Freedom from motion, agitation, or disturbance; a cessation
   or absence of that which causes motion or disturbance, as of
   winds or waves; tranquility; stillness; quiet; serenity.
   [1913 Webster]

         The wind ceased, and there was a great calm. --Mark.
                                                  iv. 39.
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         A calm before a storm is commonly a peace of a man's
         own making.                              --South.
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The Collaborative International Dictionary of English v.0.48:

Calm \Calm\, v. i. [imp. & p. p. Calmed (k[aum]md); p. pr. &
   vb. n. Calming.] [Cf. F. calmer. See Calm, n.]
   1. To make calm; to render still or quiet, as elements; as,
      to calm the winds.
      [1913 Webster]

            To calm the tempest raised by Eolus.  --Dryden.
      [1913 Webster]

   2. To deliver from agitation or excitement; to still or
      soothe, as the mind or passions.
      [1913 Webster]

            Passions which seem somewhat calmed.  --Atterbury.

   Syn: To still; quiet; appease; allay; pacify; tranquilize;
        soothe; compose; assuage; check; restrain.
        [1913 Webster]

WordNet (r) 3.0 (2006):

calm
    adj 1: not agitated; without losing self-possession; "spoke in a
           calm voice"; "remained calm throughout the uproar"; "he
           remained serene in the midst of turbulence"; "a serene
           expression on her face"; "she became more tranquil";
           "tranquil life in the country" [syn: calm,
           unagitated, serene, tranquil]
    2: (of weather) free from storm or wind; "calm seas" [ant:
       stormy]
    n 1: steadiness of mind under stress; "he accepted their
         problems with composure and she with equanimity" [syn:
         composure, calm, calmness, equanimity] [ant:
         discomposure]
    2: wind moving at less than 1 knot; 0 on the Beaufort scale
       [syn: calm air, calm]
    v 1: make calm or still; "quiet the dragons of worry and fear"
         [syn: calm, calm down, quiet, tranquilize,
         tranquillize, tranquillise, quieten, lull, still]
         [ant: agitate, charge, charge up, commove,
         excite, rouse, turn on]
    2: make steady; "steady yourself" [syn: steady, calm,
       becalm]
    3: become quiet or calm, especially after a state of agitation;
       "After the fight both men need to cool off."; "It took a
       while after the baby was born for things to settle down
       again." [syn: calm, calm down, cool off, chill out,
       simmer down, settle down, cool it]
    4: cause to be calm or quiet as by administering a sedative to;
       "The patient must be sedated before the operation" [syn:
       sedate, calm, tranquilize, tranquillize,
       tranquillise] [ant: arouse, brace, energise,
       energize, perk up, stimulate]