horizon

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The apparent intersection of the earth and sky as seen by an observer. Also called apparent horizon.
2. n. Astronomy The sensible horizon.
3. n. Astronomy The celestial horizon.
4. n. Astronomy The limit of the theoretically possible universe.
5. n. The range of one's knowledge, experience, or interest.
6. n. Geology 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.
7. n. Geology A specific layer of soil or subsoil in a vertical cross section of land.
8. n. Archaeology A period during which the influence of a specified culture spread rapidly over a defined area: artifacts associated with the Olmec horizon in Mesoamerica.

Century Dictionary and Cyclopedia

1. n. The circle which at sea forms the apparent boundary between sea and sky, and on land would bound the sky were all terrestrial obstructions down to the sea-level removed. Called the apparent, sensible, or visible horizon, in distinction from the astronomical horizon (which see, below).
2. n. Hence The line that bounds the view; the limit of vision.
3. n. Figuratively, the limit of intellectual perception, of experience, or of knowledge.
4. n. In geology, a stratum or group of strata characterized by the presence of a particular fossil not found in the underlying or overlying beds, or of a peculiar assemblage of fossils. Such a bed or series of beds is often designated as the zone of the fossil or group of fossils in question, and such a distinctly marked division is sometimes called a horizon, as forming a convenient plane of reference for other groups of strata occurring above and below, and not so definitely marked by peculiar fossil contents.
5. n. In zoology and anatomy, a level or horizontal line or surface: as, the horizon of the teeth; the horizon of the diaphragm
6. To limit or bound by a horizon.

Wiktionary

1. n. The horizontal line that appears to separate the Earth from the sky.
2. n. The range or limit of one's knowledge, experience or interest.
3. n. geology A specific layer of soil or strata
4. n. archaeology, US A cultural sub-period or level within a more encompassing time period.

GNU Webster's 1913

1. n. The line which bounds that part of the earth's surface visible to a spectator from a given point; the apparent junction of the earth and sky.
2. n. A plane passing through the eye of the spectator and at right angles to the vertical at a given place; a plane tangent to the earth's surface at that place; called distinctively the sensible horizon.
3. n. A plane parallel to the sensible horizon of a place, and passing through the earth's center; -- called also rational horizon or celestial horizon.
4. n. (Naut.) The unbroken line separating sky and water, as seen by an eye at a given elevation, no land being visible.
5. n. (Geol.) The epoch or time during which a deposit was made.
6. n. (Painting) The chief horizontal line in a picture of any sort, which determines in the picture the height of the eye of the spectator; in an extended landscape, the representation of the natural horizon corresponds with this line.
7. n. The limit of a person's range of perception, capabilities, or experience.
8. n. A boundary point or line, or a time point, beyond which new knowledge or experiences may be found.

WordNet 3.0

1. n. a specific layer or stratum of soil or subsoil in a vertical cross section of land
2. n. the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth
3. n. the line at which the sky and Earth appear to meet
4. n. the range of interest or activity that can be anticipated