"horizon" in the noun sense
1. horizon, apparent horizon, visible horizon, sensible horizon, skyline
the line at which the sky and Earth appear to meet
2. horizon, view, purview
the range of interest or activity that can be anticipated
"It is beyond the horizon of present knowledge"
3. horizon
a specific layer or stratum of soil or subsoil in a vertical cross section of land
4. horizon, celestial horizon
the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth
Source: WordNet® (An amazing lexical database of English)
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