n 1  :  a body partition of muscle and connective tissue : specif  :  the partition separating the chest and abdominal cavities in mammals - see PELVIC DIAPHRAGM UROGENITAL DIAPHRAGM   2  :  a device that limits the aperture of a lens or optical system  3  :  a molded cap usu. of thin rubber fitted over the uterine cervix to act as a mechanical contraceptive barrier .
 
 
 
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