Octameter in poetry is a line of eight metrical feet. It is not very common in English verse. E.g: -

Trochaic

Once upon a midnight dreary, while I pondered, weak and weary

Over many a quaint and curious volume of forgotten lore-

While I nodded, nearly napping, suddenly there came a tapping

As of some one gently rapping, rapping at my chamber door

(Edgar Allen Poe, "The Raven")

Anapaestic

Ere frost-flower and snow-blossom faded and fell, and the splendour of winter had passed out of sight,

The ways of the woodlands were fairer and stranger than dreams that fulfil us in sleep with delight;

The breath of the mouths of the winds had hardened on tree-tops and branches that glittered and swayed

Such wonders and glories of blossomlike snow or of frost that outlightens all flowers till it fade

(A. C. Swinburne, "March: An Ode")