Bone cavity is a term used to describe the hollow spaces in bones. The crossword solutions for this term include antrum (6 letters), SINUS (5 letters), fossa (5 letters), antra (5 letters), and MOLAR (5 letters). An antrum is a large cavity in the skull, while a SINUS is an air-filled cavity in the skull. A fossa is a shallow depression or cavity in a bone, and antra are plural for antrum. Lastly, a MOLAR is a tooth with a broad, flat surface.