From Middle English diafragma,^[1][2] Ancient Greek διάφραγμα (diáphragma, “partition”), from διά (diá, “across”) and φράγμα (phrágma, “barrier”), from the verb φράσσω (phrássō). First attested in the late 14th century.^[1]

• IPA^(key): /ˈdaɪəˌfɹæm/

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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.

   thoracic diaphragm;   pulmonary 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.

   Hypernyms: contraceptive < device

   Coordinate terms: internal condom, female condom (not to be confused); external condom, male condom; condom; IUD, intrauterine device

   cervical diaphragm;   contraceptive diaphragm

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.
   • 1847, editorial staff, “Improvement in Water Taps, Cister Valves, &c. ”, in Scientific American, series 1, Volume 3, Issue 9, page 68:

     This is effected by a novel and ingenious application of two flexible diaphragms—the upper of which, being acted upon by the lower, is pulled down on its seat, and forms a perfectly leakless joint.

   • 1994 April 5, “Two Former Biosphere Workers Are Accused of Sabotaging Dome”, in The Associated Press‎^[1]:

     There also were five broken panes of glass on the two huge, rubberlike diaphragms that equalize air pressure within the dome as the artificial atmosphere expands and contracts with temperature variations, he said.

5. (acoustics) In a speaker, the thin, semi-rigid membrane which vibrates to produce sound.

   acoustic diaphragm

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^[2], 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.

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^[3], 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^[4], →ISBN, page 16-24:

     The holes and burning are caused by the part diaphragming at 20000-40000 cycles/second.

• 👁 The thoracic diaphragm.
  
  The thoracic diaphragm.
• 👁 A mechanical diaphragm.
  
  A mechanical diaphragm.
• 👁 An acoustic diaphragm.
  
  An acoustic diaphragm.