A dumbo is a rude, informal word for someone you think is stupid. It sounds childish — the kind of name kids throw at each other — and it is unkind. Adults may say it as a joke about themselves (I felt like a dumbo) more safely than about another person. It is not a neutral classroom word, and it is not a medical word. There is a famous Disney elephant called Dumbo, which makes the insult feel cartoonish, and that is part of why it can sound both silly and sharp. Though actually that elephant is not ‘stupid’ in the story; he is the one with huge ears who learns to fly. Separately, DUMBO in New York is a neighbourhood name (from a phrase about a bridge), which has nothing to do with being thick. This entry is only the insult.