diaphragm vs rhythm method

diaphragm

noun
  • A contraceptive device consisting of a flexible cup, used to cover the cervix during intercourse. 

  • In a speaker, the thin, semi-rigid membrane which vibrates to produce sound. 

  • A thin opaque structure with a central aperture, used to limit the passage of light into a camera or similar device. 

  • Any of various membranes or sheets of muscle or ligament which separate one cavity from another. 

  • 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. 

  • 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. 

  • 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. 

  • A permeable or semipermeable membrane. 

verb
  • To reduce lens aperture using an optical diaphragm. 

  • To act as a diaphragm, for example by vibrating. 

rhythm method

noun
  • A method of natural birth control that involves counting days of a woman's menstrual cycle in order to determine when sexual intercourse is most or least likely to result in pregnancy. 

How often have the words diaphragm and rhythm method occurred in a corpus of books? (source: Google Ngram Viewer )