prime minister, the head of government in a country with a parliamentary or semipresidential political system. In such systems, the prime minister—literally the “first,” or most important, minister—must be able to command a continuous majority in the legislature (usually the lower house in a bicameral system) to remain in office. Most countries with prime ministers have two executives, a head of government (the prime minister) and a head of state (generally either a non-executive president or a hereditary monarch).
