Ordu: A Mongolian word for a khan's tent or royal enclosure, ordu is sometimes interpreted as "palace." Of course, as nomadic pastoralists and warriors, the Mongols under Genghis Khan did not build palaces. Later in the imperial period, beginning around 1220, the various divisions of the Mongols began to construct more permanent capitals. The word can also signify an important military base.
Another common usage of the term was to designate some of the divisions of the Mongol Empire, after Genghis Khan's death. For example, the Mongols who ruled Russia and parts of Eastern Europe were called the Altyny Ordu, or "Golden Horde." In fact, the English word "horde" is derived from this Mongolian term, although in English it has come to mean simply a large crowd of people, possibly including individuals with bad intentions.
The word ordu likely made its way into English and other European languages via the Slavic languages of Eastern Europe. It's not surprising that the Mongols made such an impression on the Russians; after all, they are the only people who have ever conquered Russia, and they actually preferred to attack in the winter! Under similar conditions, both Napoleon Bonaparte and the German Nazis didn't stand a chance.