Several parts combine into one character.

霧 is a phonetic-semantic compound: 雨 (rain) + 務 (wù, "to be diligent / engage in business" — providing the sound). The composite reads as "tiny rain-like droplets blanketing the air" = fog / mist. The rain radical confirms 霧 as part of the same meteorological family as 雷 (thunder), 雪 (snow), 雲 (cloud) — all atmospheric phenomena. Mainland China simplified to 雾.

Korean reading "mu." 濃霧 (nongmu, dense fog), 朝霧 (jomu, morning fog), 霧雨 (muu, mist-rain / drizzle), and the famous four-character idiom 五里霧中 (orimu-jung, "in the middle of fog five li thick" — meaning "completely lost / utterly unable to make sense of a situation"). The idiom comes from a Han dynasty story about a sage who could conjure fog five li deep around himself; it now describes any state of total confusion. Korean students memorize this idiom in middle school.

Mandarin wù, 4th tone (simplified 雾). 雾 (wù, fog), 大雾 (dàwù, heavy fog), 烟雾 (yānwù, smoke / haze), and the modern compound that has become inescapable in 21st-century Chinese: 雾霾 (wùmái, "fog-haze" = smog / heavy air pollution). 雾霾 became one of the most-used words in Chinese media and daily speech during the 2010s due to severe air quality issues in Beijing and other major cities. 雾霾天 (smog day), 雾霾警报 (smog alert) became routine vocabulary.

Japanese on-reading ム (mu) — 濃霧 (nōmu, dense fog), 朝霧 (asagiri, morning mist — using kun-reading; chōmu in formal contexts). Kun-reading きり (kiri) — 霧 (kiri, fog), 朝霧 (asagiri, morning fog — a poetic word in Japanese literature), 霧雨 (kirisame, mist-rain / drizzle — same compound as Korean 무우). Japanese mountain and seaside imagery in literature, anime, and travel writing leans heavily on 霧 vocabulary; the Mishima Yukio short story collection 霧 (Kiri) and countless haiku use the word evocatively.

Memory aid: rain (雨) plus 務 (just for the sound) — atmospheric water suspended like a thousand tiny diligent raindrops.