A wrongdoer is a person who does something wrong — something illegal, or something dishonest and unfair. Notice that the line above defines the BEHAVIOUR, but the word itself is the PERSON: 'wrong' + 'doer' = 'someone who does wrong'. The thing they do is 'wrongdoing'; the one who does it is the 'wrongdoer'. The word is formal and a little old-fashioned. You meet it in the news, in court reports, in company rules, in sermons and in moral stories — 'the wrongdoers were punished', 'we must protect victims, not wrongdoers'. In everyday speech people say 'the person who did it', 'the guilty one', 'the bad guy'. If you said 'that wrongdoer took my seat' your friends would laugh, because the word sounds too big and too serious for small things. It covers a wide range. A wrongdoer can be a criminal, but also a company that cheats its customers, or an official who takes money he should not take. The word does not say how bad the act was, only that the person is the one who did it. It also keeps a slightly moral flavour: it says 'this was wrong', not just 'this broke rule 14'.

做壞事的人、違法者、加害人（法律或新聞裡常見的正式說法；日常口語很少用）