Dictionary of Space Concepts

Short definition: 

An imaginary line in the sky running from due north to due south through the observer's location and the zenith.

Detailed Definition:

In astronomy, a meridian is an imaginary line in the sky that runs from due north to due south, passing through the observer's location and the zenith. The zenith is the point in the sky that is directly overhead. The meridian is used to measure the altitude of objects in the sky, as well as their right ascension and declination. The meridian also marks the boundary between the eastern and western halves of the sky, with objects east of the meridian being in the morning sky and those west of the meridian being in the evening sky.

Etymology:

Latin - medius ‘middle’ + dies ‘day’.

Sample Sentence(s):

"The planet Venus will cross the meridian at 8:00 pm tonight."

"The altitude of the North Star above the horizon can be measured relative to the observer's meridian."

"The meridian passage of a celestial object is the time it crosses the observer's meridian."

Translations:

French:

Le Meridien

German:

Höhepunkt

Polish:

Południk

Links to videos/articles:

https://astronomy.swin.edu.au/cosmos/m/meridian

https://www.britannica.com/science/celestial-meridian