1. Anatomy A muscular membranous partition separating the abdominal and thoracic cavities and functioning in respiration. Also called midriff.

2. A membranous part that divides or separates.

3. A thin disk, especially in a microphone or telephone receiver, that vibrates in response to sound waves to produce electric signals, or that vibrates in response to electric signals to produce sound waves.

4. A contraceptive device consisting of a thin flexible disk, usually made of rubber, that is designed to cover the uterine cervix to prevent the entry of sperm during sexual intercourse.

5. A disk having a fixed or variable opening used to restrict the amount of light traversing a lens or optical system.