It was hard for me to go past the definition of a mentor from Tuesdays With Morrie (by Mitch Albom):
Maybe it was a grandparent, a teacher or a colleague. Someone older, patient and wise, who understood you when you were young and impassioned, helped you to see the world as a more profound place, and gave you sound advice to guide your way through it.Equally hard for me not to include the Yoda mentor-ship of Luke from The Empire Strikes Back or this Kid President from the awesome Soul Pancake folks.
Both these sources emphasise being:
•Giving honest feedback
•Giving sound advice
That captures, for me, what a mentor truly is.