The definition of humility that most sticks with me is the following:

Humility, very simply, is the absence of arrogance. Where there is no arrogance, you relate with your world as an eye-level situation, without one-upmanship. Because of that, there can be a genuine interchange. Nobody is using their message to put anybody else down, and nobody has to come down or up to the other person's level. Everything is eye-level.

--Chögyam Trungpa, The Pocket Chögyam Trunga