I remember in school being taught a literary device while studying Beowulf where a name is replaced by a description ("wave-rider" instead of boat, a weapon being "life-ender", etc). I cannot for the life of me remember what it's called.
This is commonly called an epithet:
1a: a characterizing word or phrase accompanying or occurring in place of the name of a person or thing
You may also be thinking of a kenning:
: a metaphorical compound word or phrase (such as swan-road for ocean) used especially in Old English and Old Norse poetry