Humbleness is a standard word but one now rarely used. It denotes a state of feeling inferior or insignificant, of holding oneself low in rank, position, and importance. Humility is as much overused as humbleness is neglected; it means about what humbleness does: a modest estimate of one's rank or significance. Humility suggests acceptance of one's low station, whereas humbleness merely identifies that position. We acknowledge the humbleness of a man's birth and honor his humility in accepting that origin.
Dictionary of problem words and expressions. Harry Shaw. 1975.