Ileus (; from Greek εἰλεός eileós, "intestinal obstruction") is a disruption of the normal propulsive ability of the gastrointestinal tract. Although ileus originally referred to any lack of digestive propulsion, including bowel obstruction, up-to-date medical usage restricts its meaning to those disruptions caused by the failure of peristalsis, rather than by mechanical obstruction. Although certain older terms such as gallstone ileus and meconium ileus persist in usage, they are now misnomers (which does not mean that they are incorrect or obsolete, but rather that they are known to not sound like what they really are).