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.

2. (Anat.) The muscular and tendinous partition separating the cavity of the chest from that of the abdomen; the midriff.

3. (Zo["o]l.) A calcareous plate which divides the cavity of certain shells into two parts.

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.

5. (Mach.) A partition in any compartment, for various purposes.

Diaphragm pump, one in which a flexible diaphragm takes the place of a piston.

Source: Webster's Revised Unabridged Dictionary (1913)