1. offensive slang A derogatory term for a person who has an intellectual disability (formerly called mental retardation). A: "Are you still friends with that retard?" B: "Her name is Janet, and she has Down syndrome, you asshole. Why do you always have to be such an asshole?"

2. offensive slang By extension, a stupid, foolish, or dimwitted person. Bill, you retard, you left the gas running! We could have all been killed! I can't believe I forgot to pick up milk. I'm such a retard sometimes!