noun
capital city; capital; metropolis
Refers to the main city that functions as the seat of government of a country or comparable political unit. The gloss 'metropolis' is only appropriate when the city is also a major central city.
日本の首都は東京です。
The capital of Japan is Tokyo.
政府は首都に新しい庁舎を建てた。
The government built a new office building in the capital.
Also means 'capital' or administrative center, but is less common and more formal than 首都.
A Sino-Japanese compound: 首 means 'chief' or 'main,' and 都 means 'capital' or 'city.' The compound is conventionally understood as 'chief city' or 'capital.'