Noun, pl. diaphragms
1. In mammals, a sheet of muscle separating the thorax from the abdomen, contracted and relaxed in respiration to draw air into and expel air from the lungs; also called thoracic diaphragm.(wikipedia.org)
2. A dome-shaped, muscular partition separating the thorax from the abdomen in mammals. It plays a major role in breathing, as its contraction increases the volume of the thorax and so inflates the lungs. (Google Dictionary)
3. Any of various membranes or sheets of muscle or ligament which separate one cavity from another. (wikipedia.org)
4. A contraceptive device consisting of a flexible cup, used to cover the cervix during intercourse. (wikipedia.org)
5. A permeable or semipermeable membrane. (wikipedia.org)
Word origin: From Ancient Greek διάφραγμα (diáphragma, “partition”); Greek dia = across, and phragma = wall.