It means someone has a developmental disability. But that is not how people used it. They used it to call someone an idiot, 100%. If someone did something dumb, they would retort “retard”. How is that not exactly how it was/is used? Call them a bafoon, hammerhead, numskull, nincompoop, a schnook, make up a word for all I care. But to use a word that describes someone with a developmental disability should not be used as an insult. Don’t complain about there not being a substitute when there’s hundreds of options. You just seem to want to use it.
Did you mean to say “removed”? We’re talking about the word “retard”