It's often used in words related to:
* Astronomy: Sider can be found in words like siderite (a mineral containing iron), siderostat (a telescope mount), and siderophile (an element that tends to bind with iron).
* Iron: The association with stars stems from the belief that stars are made of iron. Therefore, the word sider can also be found in words like siderurgy (the art of working iron) and siderite.
While "sider" usually refers to stars or iron, it can also have other meanings depending on the context. For example, siderosis is a lung condition caused by the inhalation of iron dust.