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1. the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km): used as a unit in measuring stellar distances.
2. light-years,
a. a very great distance, esp. in development or progress: Today's computers are light-years ahead of older ones.
b. a very long time.


The distance that light travels in a vacuum in one year, equal to about 5.88 trillion miles (9.48 trillion kilometers).
Usage It is important to remember that a light-year is a measure of distance, not time. A light-year is the length of empty space that light can traverse in a year, close to six trillion miles. When scientists calculate how many light-years the stars are from Earth or from one another, they are calculating their distance, not their age.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.light-year - the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers
astronomy unit - a linear unit used for astronomical distances
light hour - the distance light travels in a vacuum in one hour; approximately one billion kilometers
light minute - the distance light travels in a vacuum in one minute; approximately 18 million kilometers
light second - the distance light travels in a vacuum in one second; approximately 300,000 kilometers


(lait) noun
1. the brightness given by the sun, a flame, lamps etc that makes things able to be seen. It was nearly dawn and the light was getting stronger; Sunlight streamed into the room.
2. something which gives light (eg a lamp). Suddenly all the lights went out.
3. something which can be used to set fire to something else; a flame. Have you got a light for my cigarette?
4. a way of viewing or regarding. He regarded her action in a favourable light.
1. having light; not dark. The studio was a large, light room.
2. (of a colour) pale; closer to white than black. light green.
verbpast tense, past participle lit (lit) , ˈlighted
1. to give light to. The room was lit only by candles.
2. to (make something) catch fire. She lit the gas; I think this match is damp, because it won't light.
ˈlightness noun
ˈlighten verb
to make or become brighter. The white ceiling lightened the room; The sky was lightening.
ˈlighter noun
something used for lighting (a cigarette etc).
ˈlighting noun
a means of providing light. The lighting was so bad in the restaurant that we could hardly see.
lighthouse noun
a building built on rocks, coastline etc with a (flashing) light to guide or warn ships.
ˈlight-year noun
the distance light travels in a year (nearly 9.5 million million kilometres).
bring to light
to reveal or cause to be noticed. The scandal was brought to light by the investigations of a journalist.
come to light
to be revealed or discovered. The manuscript came to light in a box of books at an auction.
in the light of
taking into consideration (eg new information). The theory has been abandoned in the light of more recent discoveries.
light up
1. to begin to give out light. Evening came and the streetlights lit up.
2. to make, be or become full of light. The powerful searchlight lit up the building; She watched the house light up as everyone awoke.
3. to make or become happy. Her face lit up when she saw him; A sudden smile lit up her face.
see the light
1. to be born, discovered, produced etc. After many problems his invention finally saw the light (of day).
2. to be converted to someone else's point of view etc.
set light to
to cause to begin burning. He set light to the pile of rubbish in his garden.