Several parts combine into one character.

忙 is a phonetic-semantic compound carrying philosophical weight: 忄 (heart radical) + 亡 (wáng, "to lose / be gone"). 亡 supplies the sound, but it also contributes the underlying meaning of "losing one's heart / mind to something." The composite implies that being busy means losing one's mental composure to the press of tasks — busyness is conceptualized in CJK not as productivity but as the dispersal of the heart's attention. There's a quiet philosophical critique embedded in the etymology: when you are 忙, your 心 has gone 亡.

Korean reading "mang." Korean keeps 忙 mostly in formal compounds: 多忙 (damang, very busy / overscheduled — frequently used in formal letters: 다망하신 중에 = "amid your busy schedule"), 繁忙 (beonmang, busy / hectic), 忙中閑 (mangjunghan, "leisure within busyness" — a treasured Sino-Korean concept of finding calm moments amid hectic days), 公務多忙 (gongmu damang, "official duties busy" = busy with work — formal). Everyday Korean uses native (bappeuda) for "busy."

Mandarin máng, 2nd tone. Modern Mandarin keeps 忙 in active spoken use: 忙 (máng), 很忙 (hěn máng, very busy — extremely common reply to "how are you?"), 帮忙 (bāngmáng, "to help with busy work" = to help — one of the most common verb compounds in spoken Chinese: 你能帮我一个忙吗? "Can you help me with something?"), 急忙 (jímáng, in a hurry), 忙不过来 (máng bù guò lái, "too busy to manage"). The compound 帮忙 is essential.

Japanese on-reading ボウ (bō) — 多忙 (tabō, very busy), 繁忙 (hanbō, busy / hectic), 忙殺 (bōsatsu, "killed by busyness" = overwhelmed by work — a vivid Japanese exaggeration). Kun-reading いそがしい (isogashii, "busy") — 忙しい (isogashii) is one of the most common Japanese adjectives, learned at the JLPT N4 level. The five-syllable length of isogashii makes it sound, fittingly, drawn out — as if even pronouncing "busy" takes effort. The negative 忙しくない (isogashikunai, "not busy") and the past 忙しかった (isogashikatta, "was busy") follow standard i-adjective conjugation.

Memory aid: heart (忄) plus loss (亡) — when busyness consumes you, your heart goes missing.