A native Korean compound: 날 (day, from 나다 "to come out/arise") + 씨 (a suffix historically related to "seed" or "state/condition"), together conveying the idea of "the character of the day." The suffix -씨 appears in a small cluster of weather-related nouns (e.g. 바람씨 "wind character," now rare), reinforcing the sense of atmospheric disposition.

Weather small talk is as universal in Korea as anywhere else — 날씨 is often the first topic of casual conversation and appears constantly in Korean TV forecasts, apps, and daily greetings. Note that Korean weather vocabulary is rich and precise: Koreans distinguish 맑다 (clear), 흐리다 (cloudy), 덥다 (hot), 습하다 (humid), and more, often all in a single weather report sentence.