diaphragm

noun

• 1a 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.

• 2a thin sheet of material forming a partition.
• a taut, flexible membrane in mechanical or acoustic systems.
• a thin contraceptive cap fitting over the cervix.

• 3a device for varying the effective aperture of the lens in a camera or other optical system.