Definition of: horizon

(hə·rī′zən) noun
1. The line of the apparent meeting of earth or sea and sky: called the local or visible horizon.
2. The bounds of observation or experience.
3. Astron. a The plane passing through a position on the earth's surface at right angles to the line of gravity: called the sensible horizon. b The great circle in which the sensible horizon cuts the celestial sphere: called the celestial, geometric, rational, or true horizon.
4. Geol. a A definite position in the stratigraphic column, or in the scheme of classification of strata according to age. b A bed or limited number of beds characterized by one or more distinctive fossils; a zone.
5. One of the layers in a cross–section of soil.
6. The imaginary line, taking the place of the natural horizon, in a picture of a landscape, on which is projected the point of sight of the viewer. See PERSPECTIVE. [<OF orizonte <L horizon <Gk. horizōn (kyklos) bounding (circle), ppr. of horizein bound <horos limit, bound]