Definition:Metric System/Length/Metre

Definition
The meter (UK English: metre) is the SI unit of length.

It was initially invented as $$10^{-7}$$ the distance from the Earth's equator to the North Pole (at sea level).

Since 1983, it is defined as the distance travelled by light in vacuum in $$\frac 1 {299 \, 792 \, 458}$$ of a second.

Linguistic Note
The word metre originated with the Italian scientist Tito Livio Burattini who pioneered the concept of a universal set of fundamental units. He used the term metro cattolico from the Greek μέτρον καθολικόν (métron katholikón), that is universal measure. This word gave rise to the French word mètre which was introduced into the English language in 1797.

The spelling metre is the one adopted by the International Bureau of Weights and Measures. Meter is the variant used in standard American English, but can be confused for the word for a general device used to measure something, in particular the standard household electricity meter, water meter and so on.