The difference between Stadia and Stadium

Stadia as a noun (surveying):

A or rod used by surveyors to measure differences in level, or to measure horizontal distances by sighting the stadia hairs (graduations) through a telescope.

Stadia as a noun (military):

A graduated brass triangle used to measure the distance of a target by comparison of the graduations with the heights of soldiers or horses.

Stadia as a noun:

Stadia as a noun:

Stadium as a noun:

A venue where sporting events are held.

Stadium as a noun:

An Ancient Greek racecourse, especially, the Olympic course for foot races.

Stadium as a noun (now, historical):

A Greek measure of length, being the chief one used for itinerary distances, also adopted by the Romans for nautical and astronomical measurements, equal to 600 Greek or 625 Roman feet, or 125 Roman paces, or to 606 feet, 9 inches.

Stadium as a noun:

A kind of telemeter for measuring the distance of an object of known dimensions, by observing the angle it subtends.

Stadium as a noun:

In surveying, a graduated rod used to measure the distance of the place where it stands from an instrument having a telescope, by observing the number of the graduations of the rod that are seen between certain parallel wires (stadia wires) in the field of view of the telescope.

Stadium as a noun (biology):

A life stage of an organism.