Definition
A soft iron bar placed across the poles of a permanent magnet during storage to complete the magnetic circuit and prevent the magnet from losing its strength over time.
Plain English
A small metal bar laid across the ends of a magnet when it is not being used. It gives the magnetism a path to flow through, which stops the magnet from weakening as it sits on the shelf.
Context Anchor
Seen in aircraft maintenance and electrical-system discussions, especially when handling or storing magnetized parts.
Derivation
From the everyday meaning of 'keeper' -- something that keeps or preserves. The bar 'keeps' the magnet's strength by giving its magnetic field a closed loop to travel through.
Why Pilots Care
A secure keeper prevents panels from opening in flight, avoiding foreign object damage or loss of control.
Intuition Check
Do not read “keeper” as a person who keeps something. Here it means a metal piece used to preserve a magnet’s strength.
Example Sentence 1
When the spare magneto was pulled from the parts shelf, the technician noticed the keeper was still in place across the magnet poles.
Example Sentence 2
A bent keeper on the baggage door required replacement before the next flight.