The word troika has been making a frequent appearance in articles discussing the Eurozone crisis, where it refers to a 'group of three', namely the European Union, the European Central Bank and the International Monetary Fund.
Troika is a Russian word based on the Russian word for the number 3 (три pronounced 'tree'). When used in English (especially in translations of Russian novels) it often means a sledge pulled by three horses. It means that in Russian too, but troika is also used in Russian where we might say in English the/a number three (buses etc), a three (a school mark or playing card), or a three-piece suit (jacket, trousers, waistcoat). There is an almost obsolete word in English for the number 3 on playing cards - trey. I blogged on the words for the numbers on playing cards here.