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diaphragm (n.)

late 14c., from Late Latin diaphragma, from Greek diaphragma "partition, barrier, muscle which divides the thorax from the abdomen," from diaphrassein "to barricade," from dia- "across" (see dia-) + phrassein "to fence or hedge in," which is of uncertain etymology. Beekes suggests it is a substrate word and finds "no convincing correspondence outside Greek." The native word is midriff. Meaning "contraceptive cap" is from 1933.