Octa is defined as eight.
An octopus, with eight legs, is an example of octa.
(meteorology) The fraction of the sky that is obscured by clouds, in eighths (one octa means that one eighth of the sky is obscured, two octas that one quarter is obscured, and so on).
Origin of octa
- Gr okta- < oktō, eight
From Webster's New World College Dictionary, 5th Edition