The Collaborative International Dictionary
Light-year \Light-year\, Light year \Light year\ (Astron.)
The distance over which light can travel in a year's time in a vacuum, 5.88 trillion miles (9.46 trillion kilometers); -- used as a unit in expressing stellar distances. It is more than 63,000 times as great as the distance from the earth to the sun. The star nearest to the earth's sun is about 4 light years distant.
a very large difference; -- used figuratively to express great differences (of distance, quality, time) in comparisons. ``Although having the same rank and salary, they were light-years apart in their ability to perform their jobs.''
Wiktionary
n. (alternative spelling of light year English)
Wikipedia
A light-year (or light year, abbreviation: ly) is a unit of length used informally to express astronomical distances. It is approximately 9 trillion kilometres (or about 6 trillion miles). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word year, the term light-year is sometimes misinterpreted as a unit of time.
The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications. The unit usually used in professional astrometry is the parsec (symbol: pc, approximately 3.26 light-years; the distance at which one astronomical unit subtends an angle of one second of arc).
Usage examples of "light-year".
But Altair III did indeed have intelligent life forms: it was perhaps unfortunate that first contact, light-years from here, had gone so badly, all those decades ago.
Nova Babylonia, on the planet Nova Terra around the predictably named Nova Sol, was about a hundred light-years distant from Mingulay.
Kingdom was short, only three light-years, and Beamspace transit took hardly more than twelve hours, standard.
I went to Bellatrix with the Gaijin: Gamma Orionis, three hundred and sixty light-years away.
As a result, he was the nicest man Lindsey had ever known, the nicest by light-years or by whatever measure niceness was calculated: bunches, bucketsful, gobs.
It was more than four light-years to Alpha Centauri, but fear made a long string.
In any case, no one here on Alpha Centauri can influence political events unfolding four and three-tenths light-years away.
Carried on the flood pouring through a vortex a ship is swept past many light-years to emerge into the calm cotemporal equilibrium of curvilinear space.
Continued surveillance of enormous volumes of space, millions of cubic light-years, was still being carried out by the vast network of spacegoing robots and crewed ships.
Gargantua toward a point high enough in the gravitational well to allow a hyperjump across light-years, Lissa stood in the saloon, watching the planet recede.
From these the gods learned that the octopods were a few tens of light-years away, and heading toward the Solar System.
If most quasars, as indicated by their extreme redshifts, were more than nine or ten billion light-years away in distance, then they also must be nine or ten billion years away in time, and therefore must belong to a past era of the universe.
There were only two stable stardrive speeds, three light-years per hour and twice that, with only small ships like fighters and skitters able to achieve the higher equilibrium.
Jevlen was light-years away from Gistar, and the only way of getting ships there was through black-hole toroids projected by VISAR.
Two fleets, for example, separated by light-years in normal space, must exchange information by sending ships, or uncrewed couriers, back and forth.