Horizon : həˈraɪzn̩

1 the horizon : the line where the earth or sea seems to meet the sky

 We sailed toward the horizon.
  • The sun rose slowly over/above the eastern horizon.
 2 a : the limit or range of a person’s knowledge, understanding, or experience
 Reading broadens/expands our horizons.

2 b : the limit of what is possible in a particular field or activity

 These discoveries have opened up new horizons in the field of cancer research.