WordNet sense 1 ((anatomy) a muscular partition separating the abdominal and thoracic cavities; functions in respiration):

midriff

WordNet sense 2 (a contraceptive device consisting of a flexible dome-shaped cup made of rubber or plastic; it is filled with spermicide and fitted over the uterine cervix):

pessary, contraceptive diaphragm

WordNet sense 3 (a mechanical device in a camera that controls size of aperture of the lens):

stop