Definition
Inflammation of the lining of one or more of the sinuses (the air-filled cavities in the bones of the face and skull). The inflammation causes swelling that can block the small openings connecting each sinus to the nasal passages, trapping air and mucus inside.
Plain English
A swollen, irritated condition inside the hollow spaces in the face and forehead, often caused by a cold or infection, that can block the small passages those spaces use to drain.
Context Anchor
Seen in aeromedical discussions about colds, allergies, sinus blockage, and whether a pilot is fit to fly when pressure changes are expected.
Derivation
From the Latin sinus meaning a curve, fold, or hollow, plus the medical suffix -itis meaning inflammation. So sinusitis literally means inflammation of the hollow spaces.
Why Pilots Care
Swollen sinuses trap air that cannot equalize, producing pain, possible tissue damage, or distraction that compromises safety during altitude changes.
Analogy
It is like trying to squeeze or expand air in a small sealed space. If the passage is blocked, the pressure has nowhere to go, so the pain builds as altitude changes.
Grounding Statement
Picture descending with a blocked sinus passage: the outside pressure increases, but the trapped air cannot adjust easily, so pressure builds in your face.
Intuition Check
Sinusitis is not just a stuffy nose. The key aviation issue is blocked pressure equalization in the sinus cavities during altitude changes.
Example Sentence 1
The pilot grounded himself for the week because his sinusitis would make pressure changes during climb and descent painful.
Example Sentence 2
Clearing sinusitis before the next lesson prevented pressure-related discomfort in the cockpit.