Gelid things are bitterly cold. When you wake up shivering on a winter morning, you may want to announce that you're not getting out of bed on such a gelid day.
Use this adjective to describe frozen things — like a gelid skating pond, your gelid fingers when you forget to wear your gloves, or the gelid breeze coming in through the gap under your front door. Gelid is also useful for figuratively icy things, like your teacher's gelid smile when you ask him if the class can take the day off. Gelid comes from the Latin gelidus, "icy, cold, or frosty," from gelum, "frost or intense cold."