Source : Webster's Revised Unabridged Dictionary (1913)

Deathwatch \Death"watch`\ (?; 224), n.
   1. (Zo["o]l.)
      (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}.

                She is always seeing apparitions and hearing
                deathwatches.                     --Addison.

                I did not hear the dog howl, mother, or the
                deathwatch beat.                  --Tennyson.

   2. The guard set over a criminal before his execution.

Source : WordNet®

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