Definition
An aircraft system that removes condensation, fog, or frost from the inside surface of cockpit windows by directing warm, dry air across the glass or by using an electrically heated conductive layer within the window itself.
Plain English
A system that clears fog or frost from the inside of cockpit windows so the pilot can see out clearly.
Context Anchor
Seen in cockpit heating and ventilation controls, especially during cold, wet, or humid conditions.
Derivation
From 'mist' (fine water droplets) plus the prefix 'de-' meaning 'remove.' A demister is literally a 'mist remover.' The word distinguishes the function from a defroster, which removes ice rather than condensation.
Why Pilots Care
Clear windows maintain situational awareness for safe taxi, takeoff, and landing when temperature changes cause condensation.
Analogy
It works like the defrost setting in a car, aimed at clearing the glass rather than heating the whole cabin.
Intuition Check
A window demister is not a windshield wiper. A wiper clears water from the outside; a demister clears fog or moisture from the inside surface of the window.
Example Sentence 1
Before descending into the warm, humid air below, the pilot turned on the window demister to keep the windscreen from fogging up.
Example Sentence 2
During the cold-weather preflight, the instructor verified that the window demister was working on both sides.