horizon

American  

[huh-rahy-zuhn] / həˈraɪ zən /

noun

1. the line or circle that forms the apparent boundary between earth and sky.

2. Astronomy.

   1. the small circle of the celestial sphere whose plane is tangent to the earth at the position of a given observer, or the plane of such a circle sensible horizon.

   2. Also called rational horizon.  the great circle of the celestial sphere whose plane passes through the center of the earth and is parallel to the sensible horizon of a given position, or the plane of such a circle celestial horizon.

3. the limit or range of perception, knowledge, or the like.

4. Usually horizons the scope of a person's interest, education, understanding, etc..

   His horizons were narrow.

   Synonyms:

   viewpoint, domain, perspective, world

5. Geology. a thin, distinctive stratum useful for stratigraphic correlation.

6. Also called soil horizon.  any of the series of distinctive layers found in a vertical cross section of any well-developed soil.

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horizon British  

/ həˈraɪzən /

noun

1. Also called: visible horizon.   apparent horizon.  the apparent line that divides the earth and the sky

2. astronomy

   1. Also called: sensible horizon.  the circular intersection with the celestial sphere of the plane tangential to the earth at the position of the observer

   2. Also called: celestial horizon.  the great circle on the celestial sphere, the plane of which passes through the centre of the earth and is parallel to the sensible horizon

3. the range or limit of scope, interest, knowledge, etc

4. a thin layer of rock within a stratum that has a distinct composition, esp of fossils, by which the stratum may be dated

5. a layer in a soil profile having particular characteristics See A horizon B horizon C horizon

6. likely or about to happen or appear

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horizon Scientific  

/ hə-rī′zən /

1. 1. The apparent intersection of the Earth and sky as seen by an observer.

   2. See celestial horizon

   3. See sensible horizon

2. Geology

   1. A specific position in a stratigraphic column, such as the location of one or more fossils, that serves to identify the stratum with a particular period.

   2. A specific layer of soil or subsoil in a vertical cross-section of land.

3. Archaeology A period during which the influence of a particular culture spread rapidly over a defined area.

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horizon Idioms  

1. see on the horizon.

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Other Word Forms

• horizonless adjective

Etymology

Origin of horizon

First recorded in 1540–50; from Latin horizōn, from Greek horízōn (kýklos) “bounding (circle),” equivalent to horíz(ein) “to bound, limit” + -ōn present participle suffix (nominative singular); replacing Middle English orizonte, from Middle French, from Latin horizontem, accusative of horizōn

Explanation

When you look out your window and note the furthest point you can see––the line where the sky meets the earth––that edge is called the horizon. Horizon can also mean the edge of something in a figurative sense. When you are thinking about your life, it can be difficult to get very far beyond where you are. Teenagers have a hard time imagining beyond the horizons of young adulthood. People expecting a baby often put much of their focus on infancy––having a child who can sit up or even walk is beyond the horizons of their thinking.

Example Sentences

How much you choose to invest depends on your financial objectives, time horizon and risk tolerance.

From The Wall Street Journal • Apr. 10, 2026

Given the magnitude of what is on the horizon on the pitch, all parties are understood to agree that it isn't the right time with the full focus on the season finale.

From BBC • Apr. 9, 2026

"First photo from the far side of the Moon. Captured from Orion as Earth dips beyond the lunar horizon."

From Barron's • Apr. 7, 2026

The Algodones Dunes stretch toward the horizon in pale, wind-sculpted ridges, a narrow ribbon of shifting terrain running south into Mexico.

From Los Angeles Times • Apr. 7, 2026

The sun had plunged below the horizon, taking with it every whisper of warmth from the late-autumn day.

From "The Undead Fox of Deadwood Forest" by Aubrey Hartman

Related Words

• boundary
• perspective
• prospect
• scope