The meaning of lieutenant differs in different military (see comparative military ranks), but is often subdivided into senior (first lieutenant) and junior (second lieutenant) ranks. In navies it is often equivalent to the army rank of captain; it may also indicate a particular post rather than a rank. The rank is also used in fire services, emergency medical services, security services and police forces.
Lieutenant may also appear as part of a title used in various other organisations with a codified command structure. It often designates someone who is "second-in-command", and as such, may precede the name of the rank directly above it. For example, a "lieutenant master" is likely to be second-in-command to the "master" in an organisation using both ranks.
Political uses include lieutenant governor in various governments, and Quebec lieutenant in Canadian politics. In the United Kingdom, a lord lieutenant is the sovereign's representative in a county or lieutenancy area, while a deputy lieutenant is one of the lord lieutenant's deputies.
The word lieutenant derives from French; the lieu meaning "place" as in a position (cf. in lieu of); and tenant meaning "holding" as in "holding a position"; thus a "lieutenant" is a placeholder for a superior, during their absence (compare the Latin locum tenens).
In the 19th century, British writers who considered this word either an imposition on the English language, or difficult for common soldiers and sailors, argued for it to be replaced by the calque "steadholder". However, their efforts failed, and the French word is still used, along with its many variations (e.g. lieutenant colonel, lieutenant general, lieutenant commander, flight lieutenant, second lieutenant and many non-English language examples), in both the Old and the New World.