Here's why it's a kenning:
* It's a metaphorical phrase: It doesn't literally mean "whale road" but instead describes the sea as a path for whales to travel.
* It uses imagery: The phrase evokes a picture of whales swimming through the vast ocean.
* It's a compound noun: "Whale" and "road" are combined to create a new, unique word.
Here are some other famous kennings:
* "battle-sweat" for blood
* "sky-candle" for sun
* "bone-house" for body
* "ring-giver" for king
Kennings were particularly common in Old Norse and Old English poetry, but they are also found in other Germanic languages and even occasionally in modern literature.