To provide someone with information which he or she lacks (often used with "in" or "up").
To provide with a clue.
Information which may lead one to a certain point or conclusion.
An object or a kind of indication which may be used as evidence.
Insight or understanding ("to have a clue [about]" or "to have clue". See have a clue, clue stick)
To notify or inform (someone, about something).
To caution or admonish (someone) against unwise or unacceptable behaviour.
To give warning.
To summon (someone) to or inform of a formal meeting or duty.
To advise or order to go or stay away.
To make (someone) aware of impending danger, evil, etc.