3 The rolling billows beat the ragged shore, 4 As they the earth would shoulder from her seat,
As > [As though]
5 And greedy gulf does gape, as it would eat
gulf > depths; abyss; also: chasm, ravine; perhaps: throat [?the hollow beneath a comber on the point of breaking] as > [as though]
6 Its neighbour element in its revenge:
neighbour element > (Earth and Water being two of the four elements of ancient philosophy, the others being Air and Fire)
7 Then gin the blustering brethren boldly threat
gin > do brethren > [brother waves] threat > threaten
8 To move the world from off its steadfast hinge,
hinge > axis