horizon

英[hə'raɪz(ə)n] 美[hə'raɪzn]

1. the line at which the sky and Earth appear to meet

2. the range of interest or activity that can be anticipated;

"It is beyond the horizon of present knowledge"

3. a specific layer or stratum of soil or subsoil in a vertical cross section of land

4. the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth