Answer:
The kenning used for Grendel is "shadow of death".
He is compared to an angel/ agent of death, where people die whenever they are in contact with him.
Step-by-step explanation:
Kennings are words or phrases that are used to metaphorically refer to another thing, as a form of comparison but also another name for that thing. These metaphorical compound words are used to name a person or thing in accordance with how they behave.
Lines 74-78 goes as-
That shadow of death hunted in the darkness,
Stalked Hrothgar’s warriors, old
And young, lying in waiting, hidden
In mist, invisibly following them from the edge
Of the marsh, always there, unseen
Here, the kenning used for the monster Grendel is "shadow of death". And he is compared to an angel/agent of death, waiting for its victims and following them. It could also be that whoever comes in contact with him meet their deaths.