From Chinese 票
Thanks for your comments it is very interesting to know more about the similarities of these languages.
One question though, how do you know it is from Chinese and not the other way around ?
Because China conquered Vietnam and gave them loads and loads of loanwords. The other way around, not so much.
That's not for certain. We are not even sure where the Chinese words themselves come from. Some theories suggest a more ancient tie between the Chinese and Vietnamese and that the words might have come from a common stock.
Could you suggest etymological sources / documents ?
Yeah, thanks, I love etymology, so cool to know the history of words.
As Neel says, phiếu is from Chinese 票，but 'bỏ' is indigenous Vietnamese. The Chinese use 投 'tou' as the verb for vote, which is 'đầu' in Sino-Vietnamese