Sentence:  And behind, the tempest fleet / Hurries on with lightning feet, / Riving sail, and cord, and plank, / Till the ship has almost drank / Death from the o'er-brimming deep; / And sinks down, down, like that sleep / When the dreamer seems to be / <WSD>Weltering</WSD> through eternity; 
Meaning of the word marked with <WSD> tags:  To roll around; to wallow.