Definition: always watchful
Usage: to an eye like mine, a lidless watcher of the public weal- Alfred Tennyson
Similar words: alert, watchful
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
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