horizon
noun
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the range of interest or activity that can be anticipated“It is beyond the horizon of present knowledge”view
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the line at which the sky and Earth appear to meetapparent horizonsensible horizonskyline
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the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earthcelestial horizon
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a specific layer or stratum of soil or subsoil in a vertical cross section of land