vigilant

Vigilant implies more sustained activity and more intelligent volition than alert; one may be habitually alert by reason of native quickness of perception and thought, or one may be momentarily alert under some excitement or expectancy; one who is vigilant is so with thoughtful purpose. One is vigilant against danger or harm; he may be alert or watchful for good as well as against evil; he is wary in view of suspected stratagem, trickery, or treachery. A person may be wakeful because of some merely physical excitement or excitability, as through insomnia; yet he may be utterly careless and negligent in his wakefulness, the reverse of watchful; a person who is truly watchful must keep himself wakeful while on watch, in which case wakeful has something of mental quality. Watchful, from the Saxon, and vigilant, from the Latin, are almost exact equivalents; but vigilant has somewhat more of sharp definiteness and somewhat more suggestion of volition; one may be habitually watchful; one is vigilant of set purpose and for direct cause, as in the presence of an enemy. Compare alert.