The city is served by a transit network, which includes four international airports, nine railway terminals, numerous trams, a monorail system and one of the deepest underground rapid transit systems in the world, the Moscow Metro, the fourth-largest in the world and largest outside Asia in terms of passenger numbers, and the busiest in Europe. It is recognised as one of the city's landmarks due to the rich architecture of its 200 stations.
Moscow has acquired a number of epithets, most referring to its size and preeminent status within the nation: The Third Rome (Третий Рим), The Whitestone One (Белокаменная), The First Throne (Первопрестольная), The Forty Forties (Сорок Сороков) (The Forty Soroks, "sorok" translates as forty, but here it is old name of district or parish, and "forty" in old Russian means not 40, but "great many"). Moscow is one of the twelve Hero Cities. In old Russian the word "Сорок" (forty) also meant a church administrative district, which consisted of about forty churches. The demonym for a Moscow resident is "москвич" (moskvich) for male or "москвичка" (moskvichka) for female, rendered in English as Muscovite.
The name of the city is thought to be derived from the name of the Moskva River.Finno-UgricMerya and Muroma people, who were also among the tribes which originally inhabited the area, called the river Mustajoki. It has been suggested that the name of the city derives from this term. However, there have been proposed several theories of the origin of the name of the river. The most linguistically well-grounded and widely accepted is from the Proto-Balto-Slavic root *mŭzg-/muzg- from the Proto-Indo-European *meu- "wet", so the name Moskva might signify a river at a wetland or a marsh. Its cognates include Russian: музга, muzga "pool, puddle", Lithuanian: mazgoti and Latvian: mazgāt "to wash", Sanskrit: májjati "to drown", Latin: mergō "to dip, immerse". There exist as well similar place names in Poland like Mozgawa.
The original Old Russian form of the name is reconstructed as *Москы, *Mosky, hence it was one of a few Slavic ū-stem nouns. As with other nouns of that declension, it had been undergoing a morphological transformation at the early stage of the development of the language, as a result the first written mentions in the 12th century were Московь, Moskovĭ (accusative case), Москви, Moskvi (locative case), Москвe/Москвѣ, Moskve/Moskvě (genitive case). From the latter forms came the modern Russian name Москва, Moskva, which is a result of morphological generalisation with the numerous Slavic ā-stem nouns.
However, the form Moskovĭ has left some traces in many other languages, such as English: Moscow, German: Moskau, French: Moscou, Latvian: Maskava, Ottoman Turkish: Moskov, Tatar: Мәскәү, Mäskäw, Kazakh: Мәскеу, Mäskew, Chuvash: Мускав, Muskav, etc. In a similar manner the Latin name Moscovia has been formed, later it became a colloquial name for Russia used in Western Europe in the 16th–17th centuries. From it as well came English Muscovy and muscovite.
Various other theories (of Celtic, Iranian, Caucasic origins), having little or no scientific ground, are now largely rejected by contemporary linguists.