| a combining form occurring in loanwords from Greek and Latin, where it meant “eight” (octagon; octastyle), on this model, used in the formation of compound words, and in chemical terms specialized to mean “having eight atoms” (octavalent). |
| oct- or octa- pref. Variants of octo-. |
| octo- or octa- or oct- pref. Eight: octane. [Greek okta-, oktō- (from oktō) and Latin octō- (from octō); see oktō(u) in Indo-European roots.] |
