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]