As the sibling comment already said "kai" (pronounced ke like in keg) just means "and". So it literally means 4 and 10 sides in greek. But I have often seen it written as τετραδεκάεδρο (tetradecahedron) in greek as well, so without the kai part. I'm not sure why it is 4 and 10 instead of 14 though. It would be more natural in greek that way (δεκατετράεδρο - decatetrahedron). Maybe it is for putting the distinctive part (4) first, or maybe it sounded more "poetic" like that to someone and then it stuck.

kai means "and"

I guess like asking why 120 is said "one hundred and twenty" in some dialects.

Maybe that's how 14 and 12 are written in Greek.