Plain English Meaning

Hollow spaces in the bone above your eyebrows that are filled with air and connected to your nose through small drainage holes. They need to balance their air pressure with the cabin pressure as you climb or descend.

Full Definition

Air-filled cavities located in the frontal bone of the skull, just above the eyebrows and behind the forehead. Each sinus connects to the nasal passages through a small opening, allowing air pressure inside the sinus to equalize with outside air pressure during altitude changes.

Context Anchor

Seen in aeromedical discussions about sinus problems, especially when flying with a cold, allergy, or sinus congestion.

Derivation

Frontal' comes from the Latin 'frons,' meaning forehead. 'Sinus' is Latin for 'cavity, hollow, or curve.' Together: the hollow spaces in the forehead. Knowing the location helps explain why pilots with sinus blockage often feel sharp pain in the forehead area during pressure changes.