Cavity (noun)

1. A hole or space within a solid body or surface, especially one that has been created by decay, drilling, or excavation.
2. A hole in a tooth caused by decay, which can lead to infection if not filled.

Origin:

Mid-16th century from latin "cavitas" meaning "hollow".

Examples:

1. The cavity in the old oak tree was a favorite hiding place for the children.
2. Dentists fill cavities to prevent further decay of the tooth.
3. The archaeologists found ancient artifacts in the cave's cavities.
4. The dentist said I had two cavities that needed filling.
5. The engineers had to take the cavity size into consideration while designing the part.