Cavity or chamber, often in bone, with specific meanings in some hollow organs (e.g., the pyloric end or gastric antrum of the stomach).
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 725 (https://doi.org/10.1515/pac-2015-1202)