Elbow grease

This well-known expression for hard manual work dates from the early 17th century. The allusion is to the way the elbow is used in hard polishing, rubbing or cleaning. Its first citation in 1639 was in the phrase, the smell of elbow grease, which suggests it may have started life as a jocular way of referring to sweat but very soon thereafter it took on its current meaning of any manual work requiring great effort.