An article in the times has this to say:Homer: I've never been so embarrassed! And the worst part is this is brunch so you've ruined two meals! I'll see you all at lupper.
http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/books/article2234263.eceWhereas the word “kwyjibo” is of no use whatever, the term “lupper”, coined by Homer to refer to a large, cholesterol-laden meal midway between lunch and supper, is so valuable I am amazed no one invented it before.
I've also heard "dunch", again, used jokingly.I have heard people jokingly use "linner" (a combination of lunch and dinner) if the meal is too late to be called lunch and very early to be dinner, but I do not know of a common word that is used in any serious way to describe such a meal.