Ileus: Obstruction of the intestine due to its being paralyzed. The paralysis does not need to be complete to cause ileus, but the intestine must be so inactive that food cannot pass through it, which leads to blockage of the intestine. Ileus commonly follows some types of surgery. It can also result from certain drugs, injuries, and illnesses. Regardless of the cause, ileus causes constipation and bloating. When one listens to the abdomen with a stethoscope, no bowel sounds are heard because the bowel is inactive. Also known as paralytic ileus.