悪・惡|あくaku[1]atamadaka (head-high)

1. nounevil; wickedness
   いかなる善意ぜんいの考かんがえもそれ自体じたいはあくでありうる。↗

   Any virtuous idea can be vicious in itself.
2. noun(role of) the villain (in theatre, etc.); the bad guy

• Synonym邪よこしまWrittenWritten adjectival noun for a warped mind — 「邪な考え」. A native word stressing crooked intent; 「悪」 is evil itself, the opposite of good.
• Synonym邪悪じゃあくNeutralAdjectival noun for sheer wickedness — 「邪悪な心」「邪悪な意図」. Strong enough to judge real people and deeds; 「悪」 is a plain noun.
• Synonym悪徳あくとくNeutralUnscrupulous, swindling people for gain — 「悪徳業者」. Mostly used inside compounds.
• Synonym不善ふぜんWrittenWritten word for evil or wrongdoing — 「小人閑居して不善をなす」. Mostly found in set phrases.
• Synonym邪曲じゃきょくWrittenWritten word for a crooked, wicked heart; rare — say 「邪悪」 in daily speech.
• Synonym姦悪かんあくWrittenWritten word for extreme wickedness or a wicked person; rare — say 「悪人」 in everyday speech.
• Related不義ふぎWrittenWritten word for injustice or illicit love — 「不義密通」. Mostly classical or old-fashioned.
• Related悪質あくしつNeutralAdjectival noun for something nasty and malicious — 「悪質な詐欺」. Mostly describes deeds and crimes, also shoddy quality.
• Related不法ふほうNeutralUnlawful acts — 「不法投棄」. Stresses breaking the law rather than evil itself.
• Related悪さわるさNeutralMischief and naughtiness — 「悪さをする」. Colloquial, mostly about children.
• Related不正ふせいNeutralDishonesty and cheating — 「不正アクセス」. Stresses breaking rules.
• Related不当ふとうNeutralUnjust, unreasonable treatment — 「不当解雇」. Stresses unreasonableness rather than evil.
• Related不良ふりょうNeutralPoor quality or delinquency — 「不良品」「不良少年」. Doesn't involve abstract good and evil.
• Related悪事あくじNeutralNoun for evil deeds — 「悪事を働く」. Points to concrete bad acts.
• Related悪行あくぎょうNeutralNoun for wicked acts — 「悪行の数々」. Focuses on the bad things someone has done.
• Related奸邪かんじゃWrittenWritten word for a wicked person; rare, with a classical flavor.
• Related不道徳ふどうとくNeutralImmoral conduct — 「不道徳な行い」. Stresses going against ethics.
• Related姦譎かんきつWrittenWritten word for cunning and deceit; rare — in daily speech say 「ずる賢い」.
• Related横道おうどうWrittenWritten word for crooked conduct or thinking; rare and classical — say 「悪」 or 「不正」 normally.
• Related曲悪きょくあくWrittenWritten word for a wicked character; rare — just say 「悪」 in daily use.
• Related曲事きょくじWrittenWritten word for wickedness and injustice; mostly seen in classical texts.
• Related不正行為ふせいこういNeutralUnfair practices — 「試験での不正行為」. Often means cheating.
• Related不届きふとどきNeutralReprehensible behavior — 「不届き者」. Carries an old-fashioned scolding tone.
• Antonym善ぜんNeutralAntonym: goodness and good deeds — 「善悪を問う」. The direct opposite of 「悪」.
• Antonym良りょうNeutralAntonym chiefly as the grade 「良」 in 「優・良・可」; it opposes 「悪」 only on the good-versus-bad scale, while the ethical opposite is 「善」.

Use 「悪」 for evil itself, the opposite of good, or a stage villain (「善と悪」「悪を倒す」). For malicious, nasty cases pick 「悪質」, for bad acts 「悪事」, for a crooked mind 「邪」. 「不正」 covers rule-breaking, 「不法」 law-breaking, 「不当」 unfairness, 「悪徳」 unscrupulous dealing, 「悪さ」 childish mischief, 「不良」 poor quality or delinquents. The written words 「不義」「不善」「邪曲」「姦悪」「奸邪」「姦譎」「横道」「曲悪」「曲事」 are rare and best avoided in speech. 「良」 opposes 「悪」 only on the plain good-versus-bad scale, as in quality or grades; the ethical opposite is 「善」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. （アク）倫理観りんりかんから外はずれたこと。倫理りんりに悖もとること。