Source : Webster's Revised Unabridged Dictionary (1913)

Watchful \Watch"ful\, a.
   Full of watch; vigilant; attentive; careful to observe
   closely; observant; cautious; -- with of before the thing to
   be regulated or guarded; as, to be watchful of one's
   behavior; and with against before the thing to be avoided;
   as, to be watchful against the growth of vicious habits.
   ``Many a watchful night.'' --Shak. ``Happy watchful
   shepherds.'' --Milton.

         'Twixt prayer and watchful love his heart dividing.
                                                  --Keble.

   Syn: Vigilant; attentive; cautious; observant; circumspect;
        wakeful; heedful. -- {Watch"ful*ly}, adv. --
        {Watch"ful*ness}, n.

Source : WordNet®

watchfulness
     n 1: the process of paying close and continuous attention [syn: {vigilance},
           {alertness}]
     2: vigilant attentiveness; "he keeps a weather eye open for
        trouble" [syn: {vigilance}, {weather eye}]