Metonymy is a figure of speech in which a thing or concept is referred to by the name of something closely associated with that thing or concept. The location of a capital is often used as a metonym for a government or other official institutions—for example: Brussels for the institutions of the European Union, The Hague for the International Court of Justice, Nairobi for the government of Kenya, Washington, D.C., for the federal government of the United States, or Beacon Hill for the government of the U.S. state of Massachusetts.
這是一種修辭手法——轉喻metonymy，即用一名稱來指代相關事物。我們來看看Wikipedia針對metonymy給出的解釋：
Metonymy is a figure of speech in which a thing or concept is referred to by the name of something closely associated with that thing or concept. The location of a capital is often used as a metonym for a government or other official institutions—for example: Brussels for the institutions of the European Union, The Hague for the International Court of Justice, Nairobi for the government of Kenya, Washington, D.C., for the federal government of the United States, or Beacon Hill for the government of the U.S. state of Massachusetts.為什麼用首都指稱國家或政府呢？因為一個國家的首都是其政府所在地，因而常用首都指稱國家或者政府。