king (n.)
use when it is the correct formal title. For example, in 1644, Christina was proclaimed king, not queen, of Sweden. Otherwise, consider using monarch, ruler, sovereign, crowned head, majesty, regent, chief of state, leader, governor, chieftain, potentate, commander, protector; autocrat, tyrant, despot, dictator; figurehead. In religious writings, sovereign is often used for God as King. For its meaning as a superlative, use best, top, expert, superstar, boss, chief, leading light, dean, mogul, nabob, tycoon, high-muck-a-muck, big wheel, big cheese.
