Statsminister is the local title for the function of prime minister in Denmark, Norway, Sweden and Finland (in Finland Swedish). Although it literally means 'state minister', it should not be confused with the English title Minister of State, which usually indicates a subordinate minister, or the French Ministre d'État which is used as a honorific.
The title statsminister has been given to the head of government in Denmark, Norway, Sweden and Finland since the late 19th or early 20th century:
The title itself was first used in Sweden in the 1809 Instrument of Government, which reduced the power of the king and saw the introduction of two ministers answerable to the Swedish Parliament: the justitiestatsminister ("Statsminister of Justice", i.e. Minister of Justice) and the statsminister för utrikes ärendena ("Statsminister for Foreign Affairs", i.e. Minister of Foreign Affairs). In 1876, Sweden's first non-royal head of government was appointed, with the title statsminister. Consequently, the prefix "stats" was dropped from the other two titles, to show that they were subordinate to the new head of government.
In Norway, which was in a union with Sweden from 1814 to 1905, a similar reform was proposed already in 1859, but the title statsminister for the head of government wasn't adopted until 1884.
In Denmark, the head of the government was titled premierminister (i.e. prime minister) from 1848 to 1854, and konseilspræsident ([i.e. President of the Council of Ministers) from 1855 to 1918, when the title was changed to statsminister in line with the practice in neighbouring Sweden and Norway.
When Finland declared itself independent from Russia at the end of 1917, governmental titles were kept from the local government of the Grand Duchy of Finland, but in 1919 it was decided that the titles in Swedish should follow the terminology of Sweden and the other Scandinavian countries, instead of being associated with the former Russian rule.