Rotter is a derogatory term for someone who behaves badly or dishonestly. Synonyms for rotter include scoundrel, cad, rogue, rascal, scalawag, villain, and blackguard. These words all imply an individual who is untrustworthy, immoral, or deceitful. Other synonyms for rotter are ne'er-do-well, miscreant, knave, and black sheep. These words describe someone who is unscrupulous, unreliable, and generally unpleasant. Rotters are often seen as lacking in character and honor, and are not to be trusted. While there may be variations in meaning between these synonyms, they all describe somebody who is not to be admired, respected, or emulated in any way.