Lieutenant - Wikipedia

A Lieutenant is a military or paramilitary officer. The word lieutenant derives from French; the lieu meaning "place" ? as in "in place of"; "in lieu of" - and "tenant" from "holding". In French history, "lieutenant du roi" was a title borne by the officer sent with military powers to represent the king in certain provinces. It is in the sense of a deputy that it has entered into the names of more senior officers, Lieutenant General, Lieutenant Colonel, and Lieutenant Commander[?].

The word is pronounced loo-tenant in American English and usually lef-tenant in British English although this is only correct with respect to the British Army. The Royal Navy pronounce the word as l'tenant which is a closer anglicised approximation of the original French. In Canada, lef-tenant is standard for all branches of the Armed Forces and for other usages such as lieutenant governor. The British pronunciation is prevalent during 14th and 15th centuries with the word being variously spelled as lieftenant, lyeftenant or luftenant It may have originated from a mistaken reading of the 'u' as a 'v'. Lev-tenant eventually becoming lef-tenant.

Originally, this was generally applied to what we today call just plain Lieutenant, who was taking the place of the Captain, who was the officer who actually raised the company of soldiers. The lieutenant's job was to lead the soldiers into battle so that the captain would not have to.

Most militaries have two types of Lieutenant:

1st Lieutenant (Ger. Oberleutnant) (Russian Senior Lieutenant)
2nd Lieutenant (Ger. Leutnant)

Sometimes the rank of 3rd Lieutenant is used, typically as a cadet or temporary rank indicating that the holder is a commissioned officer in the chain of command -- barely.

Note that a naval 1st Lieutenant is equivalent in rank to an army Captain, and a naval 2nd Lieutenant is equivalent in rank to an army 1st Lieutenant. See Comparative military ranks