Which term describes an interior cavity within a bone?

The term that describes an interior cavity within a bone is "sinus." In anatomical terms, a sinus refers specifically to an air-filled space or cavity within a bone, particularly in the context of the skull. The sinus serves various purposes, including reducing the weight of the skull, creating resonance for the voice, and providing a buffer against trauma.

In contrast to sinus, other terms like fossa refer to a depression or hollow area in a bone, not a cavity. Cavity is a more general term that can refer to any hollow space within the body but is not specific to bone anatomy. Fissure denotes a narrow slit or an opening, typically found between two parts of a bone, and does not imply an air-filled space. These distinctions illustrate the specific use of "sinus" in this context as the correct answer.