element Di is a chemical element listed on the periodic table, a transuranic element in the hypersonic series. (TNG:"Rascals")
- This element was listed on the periodic table visible in the schoolroom, although it was listed with the name "princessium," and its atomic number was listed as 87, an apparent error for conflicting with the real life element francium. The display was filled with many in-jokes, this element was apparently named for the late Princess Diana.