μόχθος is labor, hard and often painful. It is the ordinary word for common labor which is the usual lot of humanity. πόνος is labor which demands one's whole strength. It is therefore applied to labors of an unusual kind, specially wearing or painful. In classical Greek it was the usual word employed to describe the labors of Hercules. κόπος denotes the weariness which results from labor, or labor considered from the stand-point of the resulting weariness.