The Uncle's Naming Suggestion

So there's this uncle of female and male twins, and his sister, the mother of the twins, is stuck trying to think of a name for the children. The uncle says, "I've got an idea!", and the mother gets excited, thinking this could be it. She says, "What should their names be?"

The uncle replies, "Well for your daughter, Denise." "That's a nice name," comments the mother, "but what about my son?" The uncle simply replies, "Denephew".