A kenning is a device used in Norse and Anglo-Saxon poetry. It is a metaphor of a distinctly Germanic heroic variety. A kenning frequently used in Anglo-Saxon Poetry is The Whale Road. This means the road on which the whale travels, namely the ocean. A memorable Norse kenning is the alliteration Sword Sweat. This means a liquid that appears on a sword when it is at work, which is blood.
Anglo-Saxon poets seem to have been comfortable using kennings that had already been used elsewhere, whereas Norse poetry valued originality more.