悪性|あくせいakusei[0]heiban (flat)

1. no-adjectivemalignant (cancer); virulent; pernicious (anemia, anaemia)
   今こん悪性あくせいの風邪かぜがまん延えんしている。↗

   A bad cold is going about now.

• Related意地悪いじわるNeutralDescribes a person who is deliberately mean or nasty — a character trait. 「悪性」 describes diseases, inflation, etc. whose nasty nature has serious consequences.
• RelatedひどいCasualColloquial and very broad, covering anything cruel, severe or terrible. 「悪性」 modifies nouns for something nasty in nature and hard to deal with, as in 「悪性腫瘍」.
• Related有害ゆうがいNeutralRefers to things harmful to health or the environment, as in 「有害物質」. 「悪性」 describes the thing itself as nasty in nature, hard to treat or deal with.
• Related意地悪いいじわるいNeutralAn adjective for a twisted nature that enjoys teasing or tormenting others. 「悪性」 is generally not used for people's character.
• Antonym良性りょうせいNeutralThe antonym: benign, describing a tumor or condition as favorable in nature and curable. The two are paired in medical diagnoses, as in 「良性腫瘍」.

Use 「悪性」 for tumors, diseases, inflation, etc. whose nasty nature makes them hard to deal with; its antonym is 「良性」. For a mean-spirited person use 「意地悪」 or 「意地悪い」, and for things harmful to health use 「有害」.

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

1. 病気びょうきなどが治療ちりょうが困難こんなんであること、又または、放置ほうちすると重大じゅうだいな結果けっかを引き起ひきおこす病気びょうきなどの性質せいしつ。予後よごが悪わるいこと。