n.1 a muscular partition separating the thorax from the abdomen in mammals.
2 a partition in animal and plant tissues.
3 a disc pierced by one or more holes in optical and acoustic systems etc.
4 a device for varying the effective aperture of the lens in a camera etc.
5 a thin contraceptive cap fitting over the cervix.
6 a thin sheet of material used as a partition etc.
Phrases and idioms:
diaphragm pump a pump using a flexible diaphragm in place of a piston.
Etymology: ME f. LL diaphragma f. Gk (as DIA-, phragma -atos f. phrasso fence in)