Question

what is meant by sea that line hath never sounded​

Answer 1

Answer:

It is the final stanza of the poem “The River”.  

The final stanza of the poem is as follows:  

          sea that line hath never sounded  

            sea that line hath never rounded

In this final stanza the poet addresses the river as headlong river as it is joining with sea in all its quietness. Since it is now fitting together the eternal peace of sea.