noun

1. the line where the sky seems to meet the earth
2. the limit or extent of one's outlook, experience, interest, knowledge, etc. travel broadens one's horizons
3. an archaeological level or an area of culture as indicated by surviving artifacts
4. Astron. the great circle on the celestial sphere perpendicular to the line from the observer's zenith to the nadir
5. Geol. a layer of soil or rock identified by physical characteristics, particular fossils, etc.

Etymology: altered (after L) < ME orizont < OFr orizonte < L horizon < Gr horizōn (kyklos), the bounding (circle), horizon < prp. of horizein, to bound, limit < horos, boundary, limit, akin to L urvus, city boundary, orig., furrow around city