horizon (
http://definr.com/horizon)
n 1: the line at which the sky and Earth appear to meet [syn: {apparent
horizon},
visible horizon,
sensible horizon,
skyline]
2: the range of interest or activity that can be anticipated;
"It is beyond the horizon of present knowledge" [syn:
view,
purview]
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
[syn:
celestial horizon]