a hole or empty space inside something solid 洞；孔；窟窿；腔 the abdominal cavity 腹腔 the nasal cavity 鼻腔
a hole in a tooth （齲齒的）窩洞，洞 Most dentists fill cavities right away. 大多數牙醫發現蛀牙就馬上填補。
Word Originmid 16th cent.: from French cavité or late Latin cavitas, from Latin cavus ‘hollow’.