This is a GREAT activity to get your students' brains going. Most of them will probably whine about how difficult it is, but the activity truly forces students to make connections and learn material at a deeper level.
My word splash uses 40 vocab words from the Ecology unit that I teach to my Biology class. You can easily change this to fit any vocab for any unit and any subject. Students have to pick words and group them, explain why they are grouped, and then choose and explain a bonus word that fits into the category as well.
There is no one right answer to this activity. You will see some really neat creativity, and you'll also be able to pinpoint misconceptions.
I include a link on the worksheet that leads to a video; in the video, I use a screencast to show how to complete the activity.
Again, feel free to modify as needed! It can be adapted to any class, any grade level, any subject!