The faculty of choosing and holding to it. Also what is set down for after one's death — both are a person's intent made to outlast a moment.
Old English willa (desire, wish, determination), from Proto-Germanic *wiljon, named the faculty of choosing and holding to it, and a person's intent set down to outlast a moment.
The faculty of choosing and holding to a choice, and, in its other sense, what a person sets down to outlast their own death, both an intent made to survive a single moment.