The Collaborative International Dictionary of English v.0.48:

Mourning \Mourn"ing\, n. [AS. murnung.]
   1. The act of sorrowing or expressing grief; lamentation;
      sorrow.
      [1913 Webster]

   2. Garb, drapery, or emblems indicative of grief, esp.
      clothing or a badge of somber black.
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            The houses to their tops with black were spread,
            And ev'n the pavements were with mourning hid.
                                                  --Dryden.
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   Deep mourning. See under Deep.
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The Collaborative International Dictionary of English v.0.48:

Mourn \Mourn\ (m[=o]rn), v. i. [imp. & p. p. Mourned
   (m[=o]rnd); p. pr. & vb. n. Mourning.] [AS. murnan; akin to
   OS. mornian, OHG. mornen, Goth. ma['u]rnan.]
   1. To express or to feel grief or sorrow; to grieve; to be
      sorrowful; to lament; to be in a state of grief or
      sadness.
      [1913 Webster]

            Abraham came to mourn for Sarah, and to weep for
            her.                                  --Gen. xxiii.
                                                  2.
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   2. To wear the customary garb of a mourner.
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            We mourn in black; why mourn we not in blood?
                                                  --Shak.
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            Grieve for an hour, perhaps, then mourn a year.
                                                  --Pope.
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The Collaborative International Dictionary of English v.0.48:

Mourning \Mourn"ing\, a.
   1. Grieving; sorrowing; lamenting.
      [1913 Webster]

   2. Employed to express sorrow or grief; worn or used as
      appropriate to the condition of one bereaved or sorrowing;
      as, mourning garments; a mourning ring; a mourning pin,
      and the like.
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   Mourning bride (Bot.), a garden flower (Scabiosa
      atropurpurea) with dark purple or crimson flowers in
      flattened heads.

   Mourning dove (Zool.), a wild dove (Zenaidura macroura)
      found throughout the United States; -- so named from its
      plaintive note. Called also Carolina dove. See Illust.
      under Dove.

   Mourning warbler (Zool.), an American ground warbler
      (Geothlypis Philadelphia). The male has the head, neck,
      and chest, deep ash-gray, mixed with black on the throat
      and chest; other lower parts are pure yellow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mourning
    adj 1: sorrowful through loss or deprivation; "bereft of hope"
           [syn: bereaved, bereft, grief-stricken, grieving,
           mourning(a), sorrowing(a)]
    n 1: state of sorrow over the death or departure of a loved one
         [syn: mourning, bereavement]
    2: the passionate and demonstrative activity of expressing grief
       [syn: lamentation, mourning]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "mourning":
   anguish, bemoaning, bereavement, bewailing, black, crape, cypress,
   cypress lawn, deep mourning, desolation, despair, despondency,
   grief, grieving, heartache, howling, in mourning, keening, lament,
   lamentation, lamenting, loss, melancholy, misery, moaning,
   mourning band, sackcloth, sackcloth and ashes, sadness, sorrow,
   sorrowing, ululation, wailing, weeds, weeping, woe, woefulness,
   yew



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MOURNING. This word has several significations. 1. It is the apparel worn at
funerals, and for a time afterwards, in order to manifest grief for the
death of some one, and to honor his memory. 2. The expenses paid for such
apparel.
     2. It has been held in England, that a demand for mourning furnished to
the widow and family of the testator, is not a funeral expense. 2 Carr. & P.
207. Vide 14 Ves. 346; 1 Ves. & Bea. 364. See 2 Bell's Comm. 156.