long arm

The Japan Times Onlineにあった「海賊行為の処罰及び海賊行為への対処に関する法律」，通称「海賊法」に関する記事の見出しを採り上げます。

The long arm of the antipiracy law
Experts contend Japan has duty to catch, and try, Somali hijackers
Captured half a world away, off the coast of Oman in the Indian Ocean, four Somalis were sent to Tokyo to stand trial for piracy after a failed attempt to hijack an oil tanker. Three have already been convicted by the Tokyo District Court.
Yet not one of the 24 crew members was Japanese, and the tanker was registered in the Bahamas. The sole connection to Japan was that the ship was operated by Mitsui O.S.K. Lines.
http://www.japantimes.co.jp/news/2013/02/28/national/the-long-arm-of-the-antipiracy-law/#.US9MKhwhvO4

armはそもそも「武器」という意味のラテン語armaが由来の単語（『プログレッシブ英和中辞典』小学館）。よってarmには「力, 権力」という意味があります（『プログレッシブ英和中辞典』同上）。同辞書にはthe strong ［long］ arm of the law（法の強い力）やbeyond the (reach of the) arm of the law（法の及ぶ範囲の外で）などの用例が挙げられており，このことから「法」と共起しやすいということもわかりますね。（Koyamamoto）