Noun change

Singular
prime minister

Plural
prime ministers

  1. A prime minister is the head of government in a Westminster-style democracy.
    The Prime Minister is the leader of England.
    How many prime ministers are there in Europe?.
 
The prime minister of the United Kingdom, Winston Churchill.

Usage change

  1. When talking about a specific prime minister, prime minister is capitalised.
    The Prime Minister gave a speech today.
  2. When calling a prime minister by their title and name together, British usage is the Prime Minister, Rishi Sunak or Rishi Sunak, the Prime Minister. North American usage is Prime Minister Rishi Sunak.