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From Ancient Greek διάφραγμα (diáphragma, partition), from διά (diá, across) and φράγμα (phrágma, barrier), from the verb φράσσω (phrássō).


  • IPA(key): /ˈdaɪəˌfɹæm/
  • (file)


diaphragm (plural diaphragms)

  1. (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.
  2. (anatomy) Any of various membranes or sheets of muscle or ligament which separate one cavity from another.
  3. A contraceptive device consisting of a flexible cup, used to cover the cervix during intercourse.
  4. (mechanics) A flexible membrane separating two chambers and fixed around its periphery that distends into one or other chamber as the difference in the pressure in the chambers varies.
  5. (acoustics) In a speaker, the thin, semi-rigid membrane which vibrates to produce sound.
  6. (optics, photography) A thin opaque structure with a central aperture, used to limit the passage of light into a camera or similar device.
  7. (chemistry) A permeable or semipermeable membrane.
    • 1921, Wilder Dwight Bancroft, Applied Colloid Chemistry: General Theory[1], page 207:
      The mass of liquid transported through a porous diaphragm in a given time is directly proportional to the current.
  8. (construction) A floor slab, metal wall panel, roof panel or the like, having a sufficiently large in-plane shear stiffness and sufficient strength to transmit horizontal forces to resisting systems.

Derived terms[edit]


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diaphragm (third-person singular simple present diaphragms, present participle diaphragming, simple past and past participle diaphragmed)

  1. (optics, photography) To reduce lens aperture using an optical diaphragm.
    • 1870, D. Appleton & Co., Appletons' Annual Cyclopædia and Register of Important Events of the Year 1869[2], page 43:
      He employs an equatorial with an object-glass having a focal length of five metres, and which was diaphragmed down to eight centimetres.
  2. To act as a diaphragm, for example by vibrating.
    • 1996, Tom Drozda et al., Tool and Manufacturing Engineers Handbook, vol. VIII: Plastic Part Manufacturing[3], →ISBN, page 16-24:
      The holes and burning are caused by the part diaphragming at 20000-40000 cycles/second.