1A special administrative designation used only for Tokyo among Japan's prefecture-level divisions (東京都); in news and official contexts, "to" alone often stands for the Tokyo Metropolitan Government or Tokyo as a whole.
都は来月から新しい子育て支援制度を始める。
The Metropolitan Government will launch a new childcare support program next month.
東京都は日本の首都であり、人口も日本で一番多い。
Tokyo Metropolis is Japan's capital and has the largest population in the country.
都庁は新宿区にある高層ビルだ。
The Tokyo Metropolitan Government building is a skyscraper located in Shinjuku Ward.
都知事は都民の声に耳を傾けなければならない。
The Governor of Tokyo must listen to the voices of Tokyo residents.
2Used like a counter when enumerating Japan's top-level administrative divisions; "一都" means "one to," i.e., Tokyo. It commonly appears in phrases like 一都六県 ("Tokyo and six prefectures"), used in weather forecasts and news to refer to the greater Kanto region.
天気予報でよく「一都六県」という言葉を耳にする。
You often hear the phrase "one to, six ken" in weather forecasts.
3Means "capital city," synonymous with みやこ. In modern Japanese, using 都 alone in this sense sounds somewhat literary or old-fashioned; it mainly appears in historical contexts or set phrases like 花の都 ("the flourishing capital").
京都はかつて千年以上にわたり日本の都だった。
Kyoto was Japan's capital for over a thousand years.
パリは「花の都」と呼ばれることがある。
Paris is sometimes called "the city of flowers" (lit. "flower capital").