WordWeb Online

1. Without or unable to sleep
   "twenty watchful, weary, tedious nights";
   - insomniac, sleepless
    
2. Carefully observant or attentive; on the lookout for possible danger
   "there was a watchful dignity in the room"; "a watchful parent with a toddler in tow";
   - argus-eyed, open-eyed, vigilant, wakeful
    
3. Engaged in or accustomed to close observation
   "caught by a couple of watchful cops";
   - alert

See also: awake, fly [Brit, informal], heads-up, lidless, lively, sleepless, wary, wide-awake

Antonym: unvigilant

Encyclopedia: Watchful