It is also used by the military (or at least NATO). They use https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_...
While most of that system is a way to tag coordinates that are "simpler" than just latitude and longitude to a position, it's underlying system is also the Mercator projection. And some properties of Mercator, e.g. that it is angle-correct. So you can use UTM e.g. in Elint for direction finding.
It's not distance or area correct, but for normal infantry this is meaningless, since this only shows on large scales, but not the slow scales of infantry.
It was adopted by the US military between WWI and WWII, and similar projections were adopted by other militaries around the same time, because earlier (non-conformal) map projections led to dramatic errors when they were used for artillery targeting.
Blame the French for reinventing the wheel instead of, say, using a 1/1000th of a nautical mile as the definition of the metre. Alas, that's all water under the bridge by now.
If you want to do navigation in SI units, the UTM projections (see sibling thread) typically do positioning in metres inside each grid square.
full circle is 400 grad, so a right angle (10,000 km) is 100 grad.
Then minutes and seconds are factors of 100, so a centesimal minute is 1 km and 1 centesimal second is 10 m.
Etymology vs dictionary, I suppose.
How is it not? it's not a change to the actual distance (well, it is for a sufficient precision), but a change to the definition of the metre is exactly what it is. It's defined relative to the speed of light rather than a random platinum bar length, with the constant picked so that the actual measurement stay the same (up to a certain level of precision).