day

Modern English day comes from Old English dæġ, from Proto-Germanic *dagaz, from PIE *dʰegʷʰ- meaning "to burn, to be warm." The semantic shift is from "the hot time" or "the burning period" to "daylight hours." This is a distinctly Germanic word — most other Indo-European branches use reflexes of *dyew- (as in Latin diēs) for "day." The PIE root *dʰegʷʰ- also produced Latin fovēre "to warm" and Lithuanian degti "to burn." Within English, the same root connects to the now-archaic daw meaning "jackdaw" and possibly to the word dough through the notion of something warmed or baked. Old Norse dagr and Gothic dags are close Germanic cognates. The shift from "heat" to "daytime" makes perfect sense in a northern European context where warmth and sunlight were nearly synonymous.