A naval officer whose rank is higher than a lieutenant and below that of a commander.

(military, US) In the US Army, Air Force and Marines, holding the rank above Second Lieutenant and below Captain. Both ranks may be referred to as "Lieutenant" or as the complete forms of the ranks.

A military grade that is junior to the grade the adjective modifies: lieutenant colonel, lieutenant general, lieutenant commander.

To illuminate; to make clear.

(astronomy) A unit of length (abbreviation ly; equal to just under 10 trillion kilometres (10¹⁶ metres)) equal to the distance light travels in one Julian year; used to measure extremely large distances.

(chemistry) Water in its standard form of H₂O, containing two protium hydrogen atoms, as opposed to heavy water.

(US) The list of repairs and finish work required to complete a project, such as the construction of a building; a list of problems to correct.

A library provided essentially as a public service rather than as a commercial venture.

Faster than the speed of light in a vacuum, the theoretical speed limit for travel within the universe.

(alchemy) A substance which when drunk brings immortality: eternal life, eternal youth