n.

1. 【天】天顶[the S]
   zenith telescope

   天顶仪

   It felt as if we had traveled from nadir to zenith.

   感觉上我们好像已从天底走到了天顶。

2. 最高点；顶点；极盛时期[S1]
   Michael felt that he had already passed the zenith of his power.

   迈克觉得自己的权力已过了鼎盛期。

   Being elected class president was the zenith of my years in high school.

   当选班长是我中学时代最辉煌的时刻。

n.

1. the time at which something is most powerful or successful.
2. the point in the sky directly overhead. The opposite of nadir.
   ▸the highest point in the sky reached by a given celestial object.