This is because although the French started out with the word “grave” for kilogram (pronounced grav), it sounded too similar to the word “graf,” or earl/count, and so its usage became questionable during the French revolution, when lords and counts and earls and dukes were pretty much all but hated. The French decided the grave might be too large a measurement to be used as a base measurement anyway, so they decided to instead use one-thousandth of the grav as the base measurement, and named it “gramme.” However, they soon realized the gram was too small of a measurement, so they had to go back to the grave. But this time, instead of calling it grave, they added the “kilo-” prefix in front of gramme, and thus the kilogram was born.