Kennings are compound phrases that can replace a noun. Kennings have to have a figurative or metaphorical component—in fact, they are sometimes referred to as compressed metaphors. They are most often found in Old English and Old Norse literary works.
This is a kenning from Beowulf that refers to blood.
“Son of Ecgtheow”
It’s important to avoid misidentifying simple epithets as kennings. When the Beowulf poet uses “Son of Ecgtheow” to refer to Beowulf, this is not a kenning, as there is no figurative or metaphorical component.