The Collaborative International Dictionary of English v.0.48:

Deathwatch \Death"watch`\ (?; 224), n.
   1. (Zool.)
      (a) A small beetle (Anobium tessellatum and other allied
          species). By forcibly striking its head against
          woodwork it makes a ticking sound, which is a call of
          the sexes to each other, but has been imagined by
          superstitious people to presage death.
      (b) A small wingless insect, of the family Psocid[ae],
          which makes a similar but fainter sound; -- called
          also deathtick.
          [1913 Webster]

                She is always seeing apparitions and hearing
                deathwatches.                     --Addison.
          [1913 Webster]

                I did not hear the dog howl, mother, or the
                deathwatch beat.                  --Tennyson.
          [1913 Webster]

   2. The guard set over a criminal before his execution.
      [1913 Webster]

WordNet (r) 3.0 (2006):

deathwatch
    n 1: minute wingless psocopterous insects injurious to books and
         papers [syn: booklouse, book louse, deathwatch,
         Liposcelis divinatorius]
    2: bores through wood making a ticking sound popularly thought
       to presage death [syn: deathwatch beetle, deathwatch,
       Xestobium rufovillosum]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "deathwatch":
   agony, burial service, death agonies, death groan, death rattle,
   death struggle, death throes, deathbed, dirge, dying breath,
   eulogy, exequies, extreme unction, extremity, final extremity,
   funeral oration, funeral rites, last agony, last breath, last duty,
   last gasp, last honors, last offices, last rites, moribundity,
   obsequies, requiem, requiem mass, throes of death, viaticum,
   wake