Question

why is a line of longitude called a Meridian?​

Answer 1

Answer:

This is why prime meridian is also known as the Greenwich Meridian. In a geographical coordinate system, the Greenwich Meridian (or prime meridian) is the 0° line of longitude from which we measure 180° to the west and 180° to the east. Most coordinate systems define a zero line at the equator that runs east-west.

Answer 2

Answer:

Lines of Longitude are called this because intersect right where midday happens and Meridian means midday in Latin. :)