Spotted dick is a British-style pudding, containing dried fruit commonly served with custard. Spotted refers to the dried fruit specks throughout. The origin of "dick" is unclear, but speculation leads towards a contraction or corruption of the word "pudding," a corruption of the word "dough", dog, as "spotted dog," or the German word for "thick."
In "The Most Interesting Man in the World", Peter presents to the kids three smart words that sound dirty but aren't in order to try to keep them from giggling, including "Balzac", "Homo erectus" and "Spotted dick." The experiment ends in failure.