The Collaborative International Dictionary of English v.0.48:

Deathbed \Death"bed\, n.
   The bed in which a person dies; hence, the closing hours of
   life of one who dies by sickness or the like; the last
   sickness.
   [1913 Webster]

         That often-quoted passage from Lord Hervey in which the
         Queen's deathbed is described.           --Thackeray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deathbed
    n 1: the last few hours before death
    2: the bed on which a person dies

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "deathbed":
   agony, death agonies, death groan, death rattle, death struggle,
   death throes, deathwatch, dying breath, eleventh-hour, extremity,
   final extremity, last agony, last breath, last gasp, last-minute,
   later, moribundity, throes of death