Gymnasium \jim-NEY-zee-uhm\ , noun;
1. A building or room designed and equipped for indoor sports, exercise, or physical education
2. A place where Greek youths met for exercise and discussion
The surprising thing about this word is not that it comes from Greek (via Latin gymnasium). No, the thing that gets me about gymnasium is what it means in Greek. The word is gymnazein which literally means "to train naked" from gymnos ("naked").
Remember that next time you're in a gym.