Undercast

Part of speech: noun

Definitions

1. A cloud layer that sits below another, reducing sunlight and visibility while creating a gloomy ambiance
2. A meteorological phenomenon characterized by a layer of clouds that shields the lower atmosphere from direct sunlight
3. A type of cloud formation that lies beneath another cloud layer, causing diminished light and a somber sky while influencing weather conditions

Etymology: "Undercast" is built from two plain English parts. "Under" is an old and straightforward element meaning beneath, and "cast" comes from the Old Norse "kasta," to throw or fling, which became the English verb "cast" and carried sweeping senses of throwing, shedding, and spreading something over a surface. Put together in Middle English as "undercasten," the verb suggested something thrown or spread beneath another layer. The noun takes that picture literally. An undercast is the sheet of cloud lying beneath a higher layer or beneath the observer, so that a pilot or hiker looking down sees a flat white or grey surface rather than the ground. It is a term that works from the viewpoint of the observer, which is why it describes clouds sitting below the sky above rather than the sky itself. The sunlight-shielding aspect follows naturally, since a continuous cloud deck blocks the lower air from direct light.