Columbo is an American television programme, and also the man at the heart of it: Lieutenant Columbo, a detective in the Los Angeles police. He looks a mess on purpose. He wears a dirty old raincoat, seems forgetful, and asks slow, polite questions — then he turns back at the door with “just one more thing,” and the clever killer realises too late that Columbo has seen everything. Peter Falk played him from the late 1960s, and that coat is what most English speakers picture. People now use the name, half as a joke, for anyone who pretends to be slow and then asks the sharp question. It is a proper name, so we do not say “a columbo.”