A few minutes ago I turned on the TV and watched the final question on Jeopardy. The answer was (I paraphrase) "A condiment eaten with sushi and also eaten at Passover". Since there is no condiment satisfying both conditions, you might think that the contestants all got it wrong. Two were way off: they responded "nori" and "ginger". The one who got it "right" responded "horseradish", which Alex Trebek explained is the same thing as wasabi. It isn't.The Jeoparchive! has the answers and questions for the entire 29 December episode of Jeopardy, including the exact wording for the Final Jeopardy answer in question: "A plant called this accompanies sushi and also the Passover Seder."
As Language Log notes, horseradish and wasabi are totally different plants: Armoracia rusticana and Wasabi japonica, respectively. Both are members of the mustard family (Brassicaceae or Cruciferae), along with mustard, capers, radish, turnip, cress, cabbage, kale, broccoli, cauliflower, and Brussels sprouts.
A Dictionary of Japanese Food Ingredients & Culture by Richard Hosking says that wasabi and horseradish are similar in flavor, though wasabi is "less harsh and more aromatic." In the appendix, Hosking notes that:
Wasabi seems to lend itself to a considerable amount of commercial deception, possibly because horseradish is called seiyōwasabi (Western wasabi) or wasabi daikon (wasabi radish). The Japanese are reasonably aware of this, but abroad the true nature of the product often appears only on the label in Japanese, and many people think they are eating wasabi when actually they are eating colored horseradish.Wasabi is written as 山葵 in kanji, as わさび using hiragana, and as ワサビ using katakana. Fresh ground from the root [image], it also sometimes called hon-wasabi (true wasabi) with the kanji 本 before the hiragana or katakana spellings.
Writing about the kanji for wasabi, Language Log notes that 山 "yama" means mountain, while 葵 "aoi" means hollyhock. Although 山 can also be pronounced "san" and 葵 can also be pronounced "ki," "No matter how you try, you can't get wasabi from these components. The fact that these two Chinese characters together are read wasabi is morphologically arbitrary."
Gernot Katzer's Spice Pages has a lot of pictures and other information about wasabi, including it's name in number of different languages. Interestingly enough, in a lot of cases, then name translates to "Japanese horseradish" -- i.e., Japansk pepparrot (Swedish), Japán torma (Hungarian), and raifort du Japon (French).
- Wasabi - The Best Accompanist of Sushi gives a lot of info about wasabi, including comparisons of true vs. horseradish-based wasabi
- 山葵又称山嵛菜, which has lots of pictures of wasabi in various stages of cultivation and production
- Wasabi fact sheet from the Victoria (Australia) Farm Diversification Information Service