The Collaborative International Dictionary of English v.0.48:

Widowhood \Wid"ow*hood\, n.
   1. The state of being a widow; the time during which a woman
      is widow; also, rarely, the state of being a widower.
      [1913 Webster]

            Johnson clung to her memory during a widowhood of
            more than thirty years.               --Leslie
                                                  Stephen.
      [1913 Webster]

   2. Estate settled on a widow. [Obs.] "I 'll assure her of her
      widowhood . . . in all my lands." --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

widowhood
    n 1: the time of a woman's life when she is a widow
    2: the state of being a widow who has not remarried