Corker

That was a corker of an idea.

Yes it is, Frank. Don't you see? Laertes is to take the best of care of his friends—his proved friends, on the same principle that a wine-corker takes the best of care of his proved bottles.

Well, a body is bound to admit that for just a modest little one-line ad., it's a corker.

He had just had an absolute corker of an idea!