diaphragm

diaphragm 1 The muscle that separates the chest (thoracic) cavity from the abdomen. Contraction of the diaphragm helps to expand the lungs when one breathes in air. 2 A specially fitted contraceptive device that covers the cervix to prevent the entry of sperm. For greatest effectiveness, a diaphragm is used with spermicidal gel or cream. See also birth control; contraceptive.