Definition
An instrument that measures temperature. In aircraft, thermometers measure outside air temperature, cylinder head temperature, oil temperature, exhaust gas temperature, and carburetor air temperature, using sensing elements such as bimetallic strips, liquid-filled bulbs, thermocouples, or electrical resistance probes connected to a cockpit display.
Plain English
A device that tells you how hot or cold something is. In an aircraft, several different thermometers measure the temperature of the outside air, the engine, the oil, and other systems, and show the readings on gauges in the cockpit.
Context Anchor
Pilots may see thermometer readings on aircraft instruments, engine displays, weather reports, or preflight equipment.
Derivation
From Greek thermos (hot) and metron (measure). Literally a 'heat measurer' — a useful reminder that any gauge labeled with a temperature is a thermometer of some kind, even when it doesn't look like the household version.
Why Pilots Care
Temperature readings drive many in-flight decisions: outside air temperature affects density altitude and performance, oil and cylinder head temperatures warn of engine trouble, and carburetor air temperature signals icing risk. A pilot who reads thermometers carefully catches problems early.
Intuition Check
A thermometer in an aircraft is not just the outside air gauge — any instrument that reads a temperature (oil, cylinder head, exhaust, carburetor air) is a thermometer.
Example Sentence 1
Before takeoff on a hot day, the pilot checked the outside air temperature on the thermometer to calculate density altitude.
Example Sentence 2
Engine thermometers showed rising cylinder head temperatures during the climb.