somewhat similar to a cavalry guidon or standard, i.e. a small perhaps swallow-tailed flag. "Cornet" was an 18th-century junior cavalry officer's rank, e.g. in the Russian Army; the cornet bore the regimental standard. In like manner, the infantry rank of "ensign" applied to the junior officer who carried the regimental colors. Tom Gregg, 6 August 1997 a) a term prevalent in the 17-18thC for small swallow-tailed flags; b) alternative to GUIDON as a term for the standard of a cavalry regiment; c) Cavalry officer responsible for the standard - from a report entitled "The Dictionary of Flag Terminology", by William Crampton, Convenor; David Lister; Louis Loynes; and Miss P.M. Moyce, submitted to the Flag Section of the Heraldry Society of Great Britain (later to become the Flag Institute).
OED: - The fifth commissioned officer in a troop of cavalry, who carried the colours; corresponding to the ensign in infantry. Cornet. Dict.Gen: - The lowest commissioned rank in a cavalry regiment, equivalent to the present 2nd Lieutenant. 1260.
Cornet was the third and lowest grade of commissioned officer in a British cavalry troop, after captain and lieutenant. The cornet carried the troop standard, also known as a "cornet". This rank was known as ensign in the infantry and was one of the subaltern ranks (along with lieutenant).