horizon

noun7

1. •
   The visible horizontal line (in all directions) where the sky appears to meet the earth in the distance.

   • A tall building was visible on the whole sweep of the horizon.
   • The sky and sea seem to merge at the horizon.
2. •
   The range or limit of any dimension in which one exists.

   • Only mortality, this irreducible and primordial horizon, that very horizon which, in Being and Time, Heidegger so compellingly revealed as the unsurpassable and defining possibility, remains. — 2003
3. •
   (figurative) The range or limit of one's knowledge, experience or interest; a boundary or threshold.

   • Some students take a gap year after finishing high school to broaden their horizons.
   • With clinical researchers hard at work, a new treatment is on the horizon.
4. •
   A specific layer of soil, or stratum
5. •
   A cultural sub-period or level within a more encompassing time period.
6. •
   Any level line or surface.
7. •
   The point at which a computer chess algorithm stops searching for further moves.