Wikipedia:

Cavity

Summary:

a hole. It may refer to: Dental cavity, damage to the structure of teeth | Body cavity, a fluid filled space in many animals where organs typically develop | Cavity wall, a wall consisting of two skins with a cavity. | Resonator, a device designed to ...  (43 of 153 words, 8 senses)

Link:

http://en.wikipedia.org/wiki/Cavity  [cite]

Encarta:

cavity | cavities [plural]

Summary:

a hole or hollow space in something | a hole in a tooth, caused by decay | a hollow area inside the body  (21 of 53 words, 3 senses, 1 etymology, pronunciation)

Link:

http://encarta.msn.com/dictionary 1861595616/definition.html  [cite]

Random House:

cavity | cavities [plural]

Summary:

any hollow place; hollow. | [anatomy] a hollow space within the body, an organ, a bone, etc. | a hollow space or a pit in a tooth, most commonly ...  (27 of 49 words, 3 senses, pronunciation)

Link:

http://dictionary.infoplease.com/cavity  [cite]

Merriam-Webster:

cavity | cavities [plural]

Summary:

an unfilled space within a mass | a hollowed-out space | an area of decay in a tooth; "caries"  (17 of 45 words, 3 senses, 1 etymology, pronunciation)

Link:

http://www.merriam-webster.com/dictionary/cavity  [cite]

Wiktionary:

cavity | cavities [plural] | buccal cavity | cavity back | cavity batten | cavity coupling | cavity fill | cavity filter | cavity impedence | cavity magnetron | cavity oscillator | cavity radiator | cavity resonance | cavity tray | cavity tuning | cavity vent | cavity wall | oral cavity

Summary:

A hole or hollow depression. | A hollow area within the body (such as the sinuses). | [dentistry] A soft area in a decayed tooth.  (23 of 32 words, 3 senses, 1 etymology)

Link:

http://en.wiktionary.org/wiki/cavity  [cite]