Octa-

Octa- from Greek octa meaning 8 was an old prefix established a few years before Yotta-. It was later dropped and replaced with Yotta- beacuse it's symbol, O, could be confused with a zero.

The reciprocal of this prefix is octo-, from Latin octo meaning 8. It was also removed and replaced with Yocto- beacuse it's symbol, o, could also be too confused with a zero.