The action or process of extracting blood (from a person, animal, vein, or part of the body) for (supposed) therapeutic purposes; The drawing or ‘letting’ of blood.
"bleeding, n.". OED Online. December 2015. Oxford University Press. http://www.oed.com/view/Entry/20100?rskey=VnyHtX&result=1&isAdvanced=false (accessed December 22, 2015).
"bloodletting, n.". OED Online. December 2016. Oxford University Press. http://www.oed.com/view/Entry/20414?redirectedFrom=blood+letting (accessed February 07, 2017).