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
Main entry: 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