Definition
Sharing the same center. Two or more circles, cylinders, or shafts are concentric when they are arranged around a common centerline or axis.
Plain English
Lined up around the same center point. Picture circles inside circles, all sharing the exact same middle.
Context Anchor
Seen in aircraft maintenance descriptions, instrument diagrams, and drawings that show round parts, circular markings, or rings.
Derivation
From the Latin 'con-' meaning 'together' and 'centrum' meaning 'center.' Literally 'sharing a center.' That literal sense is exactly how the word is used in aviation -- parts built around a common center.
Why Pilots Care
Many engine and propeller parts must remain concentric to run smoothly. When a shaft or hub loses concentricity, it wobbles, vibrates, and wears unevenly -- a common cause of mechanical failure.
Analogy
Think of the rings on a dartboard. Each ring is a different size, but they all share the same center point. That is concentric.
Intuition Check
Concentric does not mean simply “round” or “near each other.” It means the round shapes share the same center point.
Example Sentence 1
The propeller hub must be concentric with the crankshaft, or the engine will vibrate badly in flight.
Example Sentence 2
Concentric circles on the approach chart represent different distances from the airport.