tank

液体を貯蔵するタンクや戦車のタンクしか知らなかったのですが "tank" と言う単語は新聞記事で時々見かけます。
例えばThe Japan Times Online Oct.11の見出し：
Nikkei tanks as fear grips Asia
The benchmark Nikkei 225 index tumbles 881.06 points, or 9.6 percent, to 8,276.43, its lowest closing level since May 2003. It was its biggest one-day percentage loss since the stock market crash of October 1987.
あるいはJuly 2の例を引用します。
Sentiment tanks in latest 'tankan'
Business sentiment among large manufacturers plummeted in June for the third straight quarter, with rising oil and raw material prices gouging into profits, the latest Bank of Japan "tankan" shows.
この "tank" の意味は載っていない辞書も多いようです。
Dictionary.com
Slang. to do poorly or decline rapidly; fail: The movie tanked at the box office.
The American Heritage Dictionary
Slang To suffer a sudden decline or failure: “Steady investors . . . kept their heads when the stock market tanked in October 1987” (Burton G. Malkiel, A Random Walk Down Wall Street 1990).
スラングとありますが経済記事の見出しでよく使われる単語なので憶えておくべきでしょう。