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®

watchful
     adj 1: carefully observant or attentive; on the lookout for
            possible danger; "a policy of open-eyed awareness";
            "the vigilant eye of the town watch"; "there was a
            watchful dignity in the room"; "a watchful parent with
            a toddler in tow" [syn: {argus-eyed}, {open-eyed}, {vigilant},
             {wakeful}]
     2: experiencing or accompanied by sleeplessness; "insomniac old
        people"; "insomniac nights"; "lay sleepless all night";
        "twenty watchful, weary, tedious nights"- Shakespeare
        [syn: {insomniac}, {sleepless}]