Cenosphere

Part of speech: noun

Definitions

1. A lightweight microsphere formed from the residual ash of burnt coal, characterized by its hollow structure and composition of silica and alumina
2. This hollow and light material arises from the combustion process of coal, often utilized for its insulating properties and in composite materials
3. A type of microsphere derived from coal ash that possesses a hollow structure, primarily composed of silica and alumina, often used in various industrial applications

Etymology: Cenospheres are the hollow glass-like balls that float to the top of coal-fired power station ash, and their name is a modern assembly from two ancient pieces. The first part, "ceno-", comes from the Ancient Greek "kenós", meaning "empty", which also gave English words such as "kenosis" and "cenotaph" in its broader family of uses. The second part is "sphere", which travelled a long road: from Ancient Greek "sphaîra" through Latin "sphaera" and Late Latin "sphēra", then through Old French, into Middle English as "spere" before the modern spelling settled in. Put together, the word simply means "empty sphere," describing a particle that is a shell with air or gas trapped inside. It was coined in English by combining these existing elements, the same way scientists formed many technical terms from classical roots in the modern era. The name therefore tells you exactly what the object is, with no metaphor or change of sense along the way.