IPA: //ɒkˈtæmɪtə//
KK: /ˈɑkˌtæmɪtər/
A line of poetry that has eight units of rhythm or beats.
The poet wrote an octameter to give the poem a unique rhythm.
Octameter → It is formed from "octa-" (from Greek "okto", meaning eight) and "meter" (from Greek "metron", meaning measure). The word refers to a line of verse consisting of eight metrical feet, hence the measurement of eight.
Think of 'eight' ('octa-') as the number of metrical feet in a line, and 'meter' as a measure — that's why octameter means a measure of eight.