The OG metric system (from the XVIII century) had no prefix for 10⁶. “Mega-” would be only formally acknowledged by the SI in 1960.
The ton units (yup, plural) backtrack all the way to a volume unit from the Middle Ages, the amount of liquid that you’d be able to put in a big arse cask*
Based on those two things, I think that the ton was standardised to 10⁶g considerably before the name “megagram” had the chance to appear, to the point that it became the default name across languages.
*I don’t know the English name for the cask [EDIT: “tun” acc. to @theplanlessman@feddit.uk ], but in Portuguese it’s “tonel”. From that “tonelada” (the unit). It used to be 800kg before the metric system though.
Two relevant details:
Based on those two things, I think that the ton was standardised to 10⁶g considerably before the name “megagram” had the chance to appear, to the point that it became the default name across languages.
*I don’t know the English name for the cask [EDIT: “tun” acc. to @theplanlessman@feddit.uk ], but in Portuguese it’s “tonel”. From that “tonelada” (the unit). It used to be 800kg before the metric system though.
FYI the English name of that cask is “tun”.
Thanks for the info. (To be honest I couldn’t be bothered to look for it.)
What units did Portugal use before metric?
I’m from Brazil but I think that the units were the same anyway. The ones that I recall are (note: approximated values)
I don’t recall the volume units, but I don’t expect them to be too different from the anglo units.