Definition
A variable resistor with two terminals used to control the amount of electric current flowing in a circuit. Turning the control changes the resistance, which in turn raises or lowers the current passing through the device being powered.
Plain English
A knob or slider that lets you turn something electrical up or down by changing how much current gets through.
Context Anchor
Seen in aircraft electrical systems, especially with cockpit lighting, panel lighting, and maintenance checks of adjustable electrical controls.
Derivation
From the Greek 'rheos' (a flow or stream) and 'statis' (regulating or setting). Literally a 'flow regulator' — which is exactly what it does to electric current.
Why Pilots Care
Rheostats control panel and instrument lighting at night. Knowing what the knob is doing helps a pilot understand why dimming lights too far or too fast can cause flicker, and why a failed rheostat shows up as lights stuck on full bright, full dim, or off entirely.
Analogy
Like the tap on a garden hose: the water (current) is always available, and the tap (rheostat) decides how much actually flows through.
Intuition Check
A rheostat is not just an on-off switch. It controls electricity gradually by changing resistance.
Example Sentence 1
The pilot turned the cockpit lighting rheostat down to preserve night vision during the cruise.
Example Sentence 2
A faulty rheostat caused the instrument panel lights to flicker during preflight.