Cornet was originally the third and lowest grade of commissioned officer in a British cavalry troop, after captain and lieutenant.
It was abolished in the Cardwell Reforms of 1871 and replaced by sub-lieutenant. It is equivalent to a modern second lieutenant. The Blues and Royals and Queen's Royal Hussars still use it to refer to their second lieutenants, although the latter is the formal rank held by these officers.
This rank was also used in other countries, e.g., in the Russian Empire, and the Prussian cavalry, before 1870.
The rank was in use by the time of the English Civil War. Among famous cornets in that conflict were George Joyce, Robert Stetson, and Ninian Beall.
It was abolished along with the purchase of commissions in the Army Reform Act of 1871, replaced by second lieutenant.
The ranks of ensign and cornet were abolished in the US Army in 1815.
The rank also existed in other nation's cavalry troops, such as those of Sweden (kornett) and Imperial Russia (корнет), and by the Continental Army in the American War of Independence. General Alexander Macomb was initially commissioned a cornet in a career in which he eventually became Commanding General of the United States Army. It is still used in the artillery and cavalry divisions of the Netherlands (kornet).