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 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.
  • 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.

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


from The American Heritage® Dictionary of the English Language, 4th Edition

[Middle English diafragma, from Late Latin diaphragma, midriff, from Greek, partition, from diaphrassein, to barricade : dia-, intensive pref.; see dia– + phrassein, phrag-, to enclose.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Ancient Greek διάφραγμα (diáphragma, "partition").


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  • ‡ The term diaphragm can also refer to a small flexible cap, usually made of rubber, that fits over the cervix and is used for contraception.

    diaphragm 2002

  • In Handbook for Scientific Photography (1977), Alfred A. Blaker wrote: As the substage diaphragm is closed, the depth of field increases (as when you close the diaphragm of your camera lens) ...

    Archive 2009-06-01 AYDIN 2009

  • (I don't think they sell directly to consumers) Their diaphragm is a slightly different diaphragm from Ortho's, and has a wider rim.

    Need a Diaphragm? Good Luck with That. aka TBTAM 2008

  • I for one think that a non-latex diaphragm is a great idea.

    Need a Diaphragm? Good Luck with That. aka TBTAM 2008

  • Yes, from what I was told, a new less allergenic diaphragm is just around the corner.

    Need a Diaphragm? Good Luck with That. aka TBTAM 2008

  • Hopefully Elaine's diaphragm is still in good shape, although she may want to cut back a bit on unnecessary usage so it doesn't wear out before the new ones are available.

    Need a Diaphragm? Good Luck with That. aka TBTAM 2008

  • The bladder size compared to the diaphragm is so much larger and has much more of a chance of developing a pinhole.

    Building Project Update for 8 March 2003 2003

  • As if my diaphragm is being played cos it make me feel a little breathless.

    One of these days… » Reloaded 2003

  • In fact, the ancient Greeks used the word “diaphragm” for both the mind and the muscle that we call the diaphragm.

    Jumpstart Your Metabolism Pam Grout 1996

  • These muscles are sometimes termed the diaphragm of the pelvis.

    XI. Splanchnology. 2e. The Abdomen 1918


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