Kenning is derived from the Old Norse word "kenna" - to know, perceive. It is a device used very frequently in Old English and Old Norse poetry, in which a compound, oftentimes indirect term is used to replace a common one: "whale-way" for the sea, "wave-horse" for a ship, "bone-house" for body, "heath-walker" for stag, "shoulder-companion" for a sword. 

Old English is known for the directness of its speech, so it should be remembered that kennings were mostly employed by scops during performance, and not by the average woman or man during everyday conversation.