What is s for length derived from?

[KayEl9]

What is "s" for length derived from?

Hello.
I would like to ask what word is the letter "s" indicating length derived from? I can't seem to find it anywhere and I don't know if it is purely arbitrary label, or if it's from some actual word. Thank you very much.

 

[arildno]

It might be from German "Streche, Strechung" or something like that.

 

[mfb]

"Strecke"="distance" or "line segment".

The german Wikipedia indicates that the latin "spatium" (~"Path") might be the origin.