cavity

noun pl. cavities

1. a hole or hollow place
2. a natural hollow place within the body: the abdominal cavity
3. a hollow place in a tooth, esp. when caused by decay
4. Electronics a space enclosed by metal and with a rodlike projection in the center, used as a resonator, as with a magnetron to produce electromagnetic waves, esp. microwaves
   also called cavity resonator

Origin: Fr cavité < LL cavitas < L cavus, hollow: see cave