Zenith (noun)

1. The highest point reached, especially by a celestial body in its daily path across the sky.
2. The time at which a celestial body is at its highest point in the sky.
3. The climax, pinnacle, or peak of something, especially of a person's career or achievements.

Origin:

Late 16th century: from french zénith, via latin from greek zenith 'point directly overhead', from zein 'to boil, be hot' (because the sun was thought to be hottest at noon).

Examples:

1. The sun reached its zenith in the sky at noon and began its descent towards the horizon.
2. The company was at its zenith, with a record-breaking year of profits and growth.
3. The actor's zenith was winning an Academy Award for his leading role in the film.
4. The empire reached its zenith in the 16th century, with a vast territory and powerful army.
5. The zenith of his success was being elected as the youngest mayor in the city's history.