Plain English Meaning
A tiny pointed shaft sitting inside a small polished cup, used so the compass card can spin almost without friction.
Full Definition
A low-friction bearing arrangement in which a hardened, polished pointed pivot rests in a small, smooth, jewel-like cup, allowing a delicate moving part to rotate freely with minimal resistance. In the magnetic compass, the float that carries the magnets is suspended on this type of mounting so it can swing easily and align with the Earth's magnetic field.
Context Anchor
Seen in magnetic compass construction when describing how the compass card is supported inside the compass case.
Derivation
The 'jewel' refers to a small piece of , polished (historically a real gemstone such as sapphire, used in fine watches) shaped into a tiny cup. The 'pivot' is the sharp, hardened that rests in that cup. Together they form a bearing that with very little , which is why this design has been used for centuries in precision instruments.