Definition: engaged in or accustomed to close observation
Usage: caught by a couple of alert cops; alert enough to spot the opportunity when it came; constantly alert and vigilant, like a sentinel on duty
Similar words: vigilant, wakeful, open-eyed, argus-eyed
Definition: carefully observant or attentive; on the lookout for possible danger
Usage: 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
Similar words: fly
Definition: (British informal) not to be deceived or hoodwinked
Similar words: wide-awake, heads-up
Definition: fully alert and watchful
Usage: played heads-up ball
Similar words: sleepless, lidless
Definition: always watchful
Usage: to an eye like mine, a lidless watcher of the public weal- Alfred Tennyson
Synonyms: watchful, insomniac, sleepless
Definition: experiencing or accompanied by sleeplessness
Usage: insomniac old people; insomniac nights; lay sleepless all night; twenty watchful, weary, tedious nights- Shakespeare
Similar words: awake
Definition: not in a state of sleep; completely conscious
Usage: lay awake thinking about his new job; still not fully awake