The Collaborative International Dictionary of English v.0.48:

Widow \Wid"ow\, v. t. [imp. & p. p. Widowed; p. pr. & vb. n.
   Widowing.]
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   1. To reduce to the condition of a widow; to bereave of a
      husband; -- rarely used except in the past participle.
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            Though in thus city he
            Hath widowed and unchilded many a one,
            Which to this hour bewail the injury. --Shak.
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   2. To deprive of one who is loved; to strip of anything
      beloved or highly esteemed; to make desolate or bare; to
      bereave.
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            The widowed isle, in mourning,
            Dries up her tears.                   --Dryden.
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            Tress of their shriveled fruits
            Are widowed, dreary storms o'er all prevail. --J.
                                                  Philips.
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            Mourn, widowed queen; forgotten Sion, mourn.
                                                  --Heber.
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   3. To endow with a widow's right. [R.] --Shak.
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   4. To become, or survive as, the widow of. [Obs.]
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            Let me be married to three kings in a forenoon, and
            widow
            them all.                             --Shak.
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WordNet (r) 3.0 (2006):

widowed
    adj 1: single because of death of the spouse