In the following lines from beowulf, what literary technique has the poet used in the underlined words?

to many it seemed
the wolf-of-the-waves had won his life

The literary techique used here is a kenning.

A kenning is a miniature riddle that usually had two parts and was frequently hyphenated. An example of a kenning from Beowulf was "dread-loom." The Anglo-Saxons used this term to refer to God's plan, making a comparison beween weaving and the awe inspired by God's plan.

"Wolf-of-the-waves" is used here to describe Grendel's mother, a beast who lived underwater.