Several parts combine into one character.

The traditional 惡 is a phonetic-semantic compound: 亞 (yà, "second / inferior" — providing the sound) + 心 (heart). The composite reads as "a twisted / inferior heart" = evil, wickedness. Three CJK regions then diverged: traditional Korea retains 惡; Japan adopted shinjitai 悪 (simplified upper component); Mainland China simplified to 恶 (different simplification). Three regions, three scripts. 悪 forms the canonical pair with 善 (good), and the compound 善悪 / 善惡 is fundamental to East Asian moral discourse.

This character is one of the cleanest CJK examples of a 破音字 (tone/reading-shifting character) where meaning splits by reading.

Korean has two readings of 惡. "ak" — for the "evil" sense: 善惡 (seonak, good and evil), 惡魔 (angma, devil), 惡人 (agin, evil person), 凶惡 (hyungak, sinister). "o" — for the "to hate / detest" sense: 嫌惡 (hyeomo, hatred / disgust), 惡寒 (ohan, chills from fever — note medical term).

Mandarin shows the identical split pattern with two pronunciations. è (4th tone, "evil") — 邪恶 (xié'è, evil), 恶劣 (èliè, vile / nasty), 罪恶 (zuì'è, sin and evil). wù (4th tone, "to hate") — 厌恶 (yànwù, to detest), 可恶 (kěwù, hateful / detestable). Mandarin and Korean preserve the same etymological bifurcation in their reading systems.

Japanese mirrors the same pattern with two on-readings. アク (aku) — 悪人 (akunin, evil person), 善悪 (zen'aku, good and evil), 悪魔 (akuma, devil), 悪意 (akui, malice). オ (o) — 嫌悪 (ken'o, hatred / aversion), 悪寒 (okan, chills). Kun-reading わるい (warui, "bad") — 悪い (warui), used colloquially: 「悪い悪い」 (warui warui, "my bad / sorry sorry") is friendly casual apology among Japanese friends, more informal than すみません.

Memory aid: a twisted (亞) heart (心) — moral distortion = evil. Pair with 善 (good). The character splits readings between "evil" (passive — being bad) and "to hate" (active — finding bad).