The Collaborative International Dictionary of English v.0.48:

Diaphragm \Di"a*phragm\, n. [L. diaphragma, Gr. ?, fr. ? to
   fence by a partition wall; dia` through + ?, ?, to fence,
   inclose; prob. akin to L. fareire to stuff: cf. F.
   diaphragme. See Farce.]
   1. A dividing membrane or thin partition, commonly with an
      opening through it.
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   2. (Anat.) The muscular and tendinous partition separating
      the cavity of the chest from that of the abdomen; the
      midriff.
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   3. (Zool.) A calcareous plate which divides the cavity of
      certain shells into two parts.
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   4. (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.
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   5. (Mach.) A partition in any compartment, for various
      purposes.
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   Diaphragm pump, one in which a flexible diaphragm takes the
      place of a piston.
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