all-sky

The compound adjective "all-sky" is a modern English formation built from two native Germanic elements. "All" derives from the Proto-Germanic allaz, carrying the fundamental sense of "whole" or "complete," which has remained remarkably stable. "Sky" originates from the Old Norse ský, initially meaning "cloud," which replaced the native Old English term heofon. Over time, its meaning expanded from "cloud" to encompass the entire celestial dome. The logic of the compound is transparently descriptive: "all-sky" literally means "pertaining to the complete sky," a concept utilized in fields like astronomy and meteorology to denote instruments, surveys, or phenomena that encompass the full celestial sphere.

Structure: all (complete) + sky (the heavens) - all: From Old English eall, meaning "entire, whole, every." It functions as an intensifier denoting completeness. - sky: From Old Norse ský, meaning "cloud." In modern English, it refers to the atmosphere and space above the earth, serving as the core noun being modified.