Answer:
Alliteration: grim and greedy he grasped
An alliteration is a literaty device in which a series of words begin with the same consonant sound. In this case, the repeated consonant sound is the "g" sound.
Kenning: the whale-path
The kenning comes from Old Norse tradition and it refers to the combination of words to create a new expression with metaphorical meaning. Here, the "whale-path" is a metaphor for the sea or the ocean.
Epithet: the Ruler-of-Man
An epithet is an adjective added to a person's name to describe, praise or criticize a part of them. Here, "Ruler-of-Man" is an epithet that is praising someone, probably a King.
Synecdoche: they drive their keels o'er the darkling wave.
A synecdoche is a figure of speech in which a term for a part of something refers to the whole. Here the word "keel," which is the structure on the base of a ship, is used to refer to the ship itself.
