OCTO- Meaning of OCTO- in English octo- BrE AmE , oct- /ɒktəʊ $ ɑːktoʊ/ prefix eight, or having eight:octagon (=a shape with eight sides)octopus (=a sea creature with eight arms) Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012