Glacial describes anything related to glaciers or ice ages, but it also means extremely slow-moving, like the glaciers themselves.

A glacier is a massive river of ice that forms over thousands of years in cold regions. Glaciers move, but so slowly that you'd never see them budge if you watched all day. They might creep forward just a few inches per year. Scientists study glacial movement to understand how these ice giants shaped valleys and mountains over millions of years. During glacial periods (ice ages), huge sheets of ice covered much of North America and Europe.

Because glaciers move so incredibly slowly, we use glacial to describe anything that takes forever. If your teacher reads your essay at a glacial pace, she's reading painfully slowly. When a line at the cafeteria moves at glacial speed, you might worry lunch will end before you get your food.

The word can also mean icy or unfriendly. A glacial stare is a cold, unwelcoming look that makes you feel shut out. When someone gives you a glacial reception, they're about as warm and welcoming as an iceberg.