Kenning is a figure of speech used in Old Norse and Anglo-Saxon poetry where a compound phrase is used to describe a person, place, or thing.
In this case, "sword-feast" is a metaphorical way to describe battle or war. It evokes the image of a feast where the "food" is bloodshed and violence.
Here's why it's a kenning:
* It uses two words combined to create a new, evocative meaning.
* It's a metaphorical substitution for a more common word.
Other examples of kennings include "whale-road" for the sea and "battle-sweat" for blood.