[skrebbel]

I spent five minutes googling for this to no avail. I really want to know this. If you're right, then why do I do my taxes in hexadecimal and not in decaheximal?

Does anyone know what "(Latin numeral)-ex" is called? I'm not even sure what term to search for :-)

Also is it even Latin? Greek, maybe? A mix?

[chronial]

They are called cardinal prefixes. https://en.wikipedia.org/wiki/Numeral_prefix

According to that page, both hexadeca- and decahexa- are valid. I think hexadeca- is more common. You gave on example, another is https://en.wikipedia.org/wiki/IUPAC_numerical_multiplier.