A somewhat literary or formal term for a wicked or untrustworthy person. Not common in everyday conversation; more likely to appear in writing or dramatic contexts.
He is portrayed as a typical villain in the novel.
The kanji 姦 means 'wicked' or 'cunning', and 人 means 'person'. The exact historical derivation is uncertain, but the compound follows a standard pattern for forming nouns describing types of people.