I. (ˈ)äk|taməd.ə(r), -mətə- adjective
Etymology: Late Latin, from Late Greek oktametros, from Greek okta- octa- + metron measure — more at measure
: having eight metrical feet
II. noun
or oc·tom·e·ter -|täm-
: a line consisting of eight metrical feet (as in Poe's “Deep into the darkness peering, long I stood ther wond'ring, fearing”)