An anatomical cavity is a hollow space within the body, often filled with air or fluid. The term ANATOMICAL CAVITY can be broken down into three parts: ANTRUM (6 letters), SINUS (5 letters), and FOSSA (5 letters). An antrum is a cavity in the body, such as the stomach or ear. A SINUS is an air-filled cavity in the skull, often connected to the nasal passages. Finally, a fossa is a shallow depression or cavity in the body, such as the pituitary fossa in the brain.