means The inner strength to control your impulses and stick to a chosen course of action, especially when temptation pulls the other way.

from A transparent compound of "will" (the faculty of deciding and intending — from Old English "willa," desire or determination, a cousin of words across the Germanic family) and "power." The pairing is a relatively modern coinage, emerging in the 19th century as thinkers grew fond of treating the mind as a machine with measurable forces — willpower being the engine that drives resolve.