buy the farm[美俚]阵亡；买下农场（死了）；突如其来的不正常死亡
关于来源，因为是美国的俚语，只有美国人比较清楚，下面是几个外国人的解释，我翻译了认为最可能的。
1.Buy the farm was originated with pilots. Mostly military.
If something from the government crashes on to a farm - like a military plane, the government 'buy the farm'. as in the land that it destroyed. The pilot is dead because of the impact...
“Buy the farm”的起源来自于飞行员。主要指军方的飞行员。如果政府部门的某件东西撞毁在农场里——例如军用飞机，政府部门就会“买下那个农场”，因为那块地已经被破坏了，而飞行员也在撞击的过程中死了……。
所以“Buy the farm”就比喻突如其来的不正常死亡，也就是阵亡了，特别是在战争中的，像第二次世界大战等。
2.To die, espescially in combat; most likely from the idea that a dead soldier's death benifit would serve to pay off his family's morgtage. Often shortened to "bought it."
3.This term was used during World War 2 whenever a Allied Pilot would have to make a crash landing into a European farm/house. WW2 pilots who did this were actually charged for the damages they caused and actually in a sense: "bought the farm"
详见：
http://www.urbandictionary.com/define.php?term=buy%20the%20farm