The zenith (UK: / ˈzɛnɪθ /, US: / ˈziːnɪθ /) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" point on the celestial sphere.

Zenith definition, the point on the celestial sphere vertically above a given position or observer.

zenith noun [C usually singular] (HIGHEST POINT) Add to word list astronomy specialized the highest point reached by a heavenly body (= any object existing in space, especially a planet, or the sun) as it travels around, or appears to travel around, another body:

Zenith developed from an Arabic phrase meaning "the way over one's head," and then traveled through Old Spanish, Medieval Latin, and Middle French before arriving in English. As long ago as the 1300s, English speakers used zenith to name the highest point in the celestial heavens, directly overhead.