the central part of a country, historically, commonly known as the capital city or the main region, where an emperor or other ruler resides / something within a country

(historical or contemporary) any of several kingdoms, empires, or states of the Chinese people

a surname

Japan

(archaic) Japan

Short for 日本国 (Nihon-koku): Japan (a country and archipelago in East Asia) / a surname

(historical) jiedushi (regional military governor in China during the Tang dynasty and the Five Dynasties and Ten Kingdoms period)

to make excellent use of, to have a good command of

good command of, full use of

to do through; to do (something) completely without giving up midway