diaphragm

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Anatomy A muscular membranous partition separating the abdominal and thoracic cavities and functioning in respiration.
• noun A membranous part that divides or separates.
• noun A thin disk, especially in a microphone or telephone receiver, that vibrates in response to sound waves to produce electric signals, or that vibrates in response to electric signals to produce sound waves.
• noun A contraceptive device consisting of a thin flexible disk, usually made of rubber, that is designed to cover the uterine cervix to prevent the entry of sperm during sexual intercourse.
• noun A disk having a fixed or variable opening used to restrict the amount of light traversing a lens or optical system.

from The Century Dictionary.

• noun A partition; something which divides or separates. Specifically
• noun In mech.: A thin piece, generally of metal, serving as a partition, or for some other special purpose: as, the vibrating diaphragm of a telephone, for the communication of transmitted sounds, A ring, or a plate pierced with a circular hole so arranged as to fall in the axis of the instrument, used in optical instruments to cut off marginal beams of light, as in a camera or a telescope.
• noun In anatomy, the midriff; the museulomembranous partition which separates the thoracic from the abdominal cavity in mammals.
• noun In cryptogamic botany, in Equisetum, a transverse partition in the stem at the node; in Selaginella and its allies, a layer separating the prothallium from the cavity of the macrospore; in Characeæ, a constriction formed by the enveloping cells near the tip of the oögonium.
• noun In conchology, a septum or shelf-like plate extending into the cavity of a shell, more or less partitioning it.
• To interpose in the path of a beam of light, or in the field of an optical instrument, a screen containing an aperture; specifically, in photography, to reduce the aperture of an objective by the use of a diaphragm.
• noun A thin ring or plate, pierced with a hole which is usually, but not always, circular.
• noun A sheet or disk of flexible material, confined at the edges, but free to yield to pressure on one side or the other: used in regulating-devices where pressure is one element, and to operate valves by a pressure from a distance.
• noun In tunnel-work, a partition separating the working-face from the first chamber.
• noun In statistical mechanics, a portion of space, separating two ensembles of systems of molecules, such that there is no interchange of particles between the two.
• noun In pathology, a membranous structure which partly or completely closes the lumen of a tube or cavity: as, inherited diaphragm of the larynx.

from the GNU version of the Collaborative International Dictionary of English.

• noun A dividing membrane or thin partition, commonly with an opening through it.
• noun (Anat.) The muscular and tendinous partition separating the cavity of the chest from that of the abdomen; the midriff.
• noun (Zoöl.) A calcareous plate which divides the cavity of certain shells into two parts.
• noun (Opt.) A plate with an opening, which is generally circular, used in instruments to cut off marginal portions of a beam of light, as at the focus of a telescope.
• noun (Mach.) A partition in any compartment, for various purposes.
• noun one in which a flexible diaphragm takes the place of a piston.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy 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.
• noun anatomy Any of various membranes or sheets of muscle or ligament which separate one cavity from another.
• noun A contraceptive device consisting of a flexible cup, used to cover the cervix during intercourse.
• noun mechanics A flexible membrane separating two chambers and fixed around its periphery that distends into one or other chamber depending on the as the difference in the pressure in the chambers varies.
• noun acoustics In a speaker, the thin, semi-rigid membrane which vibrates to produce sound.
• noun optics, photography A thin opaque structure with a central aperture, used to limit the passage of light into a camera or similar device.
• noun chemistry A permeable or semipermeable membrane
• noun construction A floor slab, metal wall panel, roof panel or the like, havig a sufficiently large in-plane shear stiffness and sufficient strength to transmit horizontal forces to resisting systems.
• verb optics, photography To reduce lens aperture using an optical diaphragm.
• verb To act as a diaphragm, for example by vibrating.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a mechanical device in a camera that controls size of aperture of the lens
• noun 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
• noun electro-acoustic transducer that vibrates to receive or produce sound waves
• noun (anatomy) a muscular partition separating the abdominal and thoracic cavities; functions in respiration