Definition
The buoyant disc or assembly inside a magnetic compass to which the magnets and compass card are attached. It floats in a fluid-filled bowl, allowing the magnets and card to pivot freely so they can align with the Earth's magnetic field.
Plain English
The small floating part inside the compass that holds the magnets and the numbered card. Because it floats in liquid, it can swing easily and point in the right direction.
Context Anchor
Seen in descriptions of how a magnetic compass is built and how the compass card is supported inside the liquid-filled compass bowl.
Derivation
Float' comes from the Old English 'flotian', meaning to rest on liquid. Here the disc literally floats in the compass fluid, which supports its weight so the magnets can pivot with very little friction.
Why Pilots Care
Keeps the compass card from pressing too hard on its support, allowing smooth and accurate heading indications without added friction.
Analogy
Think of it like a small buoy inside the compass. Its job is not to point the way by itself, but to help support the part that does.
Intuition Check
Do not think of a metal float as an outside float on the aircraft or a fuel-system float. In this context, it is an internal compass part that floats in the compass liquid.
Example Sentence 1
The compass card is mounted on the metal float, which pivots inside the fluid-filled bowl.
Example Sentence 2
If the metal float leaks, the compass card may sink slightly and produce sluggish or erratic readings.