The Collaborative International Dictionary
Octo- \Oc"to-\, Octa- \Oc"ta-\ [L. octo eight, Gr. 'oktw`, with a combining form 'okta-. Cf. Eight.] A combining form meaning eight; as in octodecimal, octolocular.
Douglas Harper's Etymology Dictionary
word-forming element, before vowels oct-, from comb. form of Latin octo "eight" (see octa-).
Usage examples of "octo-".
She drew up the article, Lake complex where UFO enthusiasts gathered to watch from the Tucson Citizen, dated the twenty-fourth of Octo- for strange craft over the mountains.