Definition
An instrument installed in an aircraft that records the cumulative time the engine (or aircraft) has been in operation. It is typically driven by an electrical signal, oil pressure, or engine vibration, and displays elapsed running time in hours and tenths of an hour.
Plain English
A small clock-like device that adds up how many hours the engine has been running, so the operator knows how much it has been used.
Context Anchor
You may see an hourmeter in the cockpit, in aircraft logbook entries, on a rental checkout sheet, or in maintenance records.
Derivation
A simple compound of 'hour' and 'meter' (from Greek 'metron', meaning a measure). Literally, a device that measures hours.
Why Pilots Care
Supplies the official engine time used to schedule required inspections and comply with airworthiness directives.
Analogy
An hourmeter is like an odometer for time instead of distance: it helps show how much use the aircraft or engine has had.
Intuition Check
Do not read hourmeter as a normal clock. It measures operating time, usually when the aircraft or equipment is running.
Example Sentence 1
Before shutdown, the pilot recorded the hourmeter reading in the aircraft logbook.
Example Sentence 2
Maintenance on the propeller was due at the next 50-hour mark on the hourmeter.