I'm with you on this Keith, the DHC is only good as far as early Morgan are concerned to me they are the same thing, I shall be most interested to read of a clear definition of each though

Well an Audi with a jigsaw is a cabriolet in the making isn't it..
There are no definitions that are consistent over time, place or manufacturer.
This page has some good definitions, but marketing has perverted these. For example Mercedes says a roadster is a sporty two seater convertible, because there's no chance their customers would accept something without wind up windows.