Plain English Meaning

A hollow space inside the bone of your cheek, just above your upper teeth, that connects to your nose through a tiny opening. If that opening gets blocked by a cold or congestion, the trapped air can cause pain when cabin pressure changes.

Full Definition

An air-filled cavity in the bone of the upper jaw, located beneath each cheek and above the upper teeth, that connects to the nasal passage through a small opening. As one of the paranasal sinuses, it is subject to pressure changes during climbs and descents and can cause facial pain if congestion blocks the opening.

Context Anchor

Seen in discussions of sinus trouble during altitude changes, especially when flying with a cold, allergy, or blocked nose.

Derivation

From the Latin maxilla, meaning 'upper jawbone,' and sinus, meaning 'a hollow' or 'curve.' So 'maxillary sinus' literally means 'the hollow in the upper jaw' -- which is exactly where it sits.

Why Pilots Care

A blocked maxillary sinus prevents pressure equalization, producing sharp facial pain on descent that can distract a or an early return to the .