poise > weight, gravity

8 And, rolling down, great Neptune does dismay;

Neptune > (See Rev. 21.1)

9 So down he fell, and like a heaped mountain lay.

111.55

The knight himselfe euen trembled at his fall,
2 So huge and horrible a masse it seem'd;
And his deare Ladie, that beheld it all,
4 Durst not approch for dread, which she misdeem'd,
But yet at last, when as the direfull feend
6 She saw not stirre, off-shaking vaine affright,
She nigher drew, and saw that ioyous end:
8 Then God she praysd, and thankt her faithfull knight,
That had atchieu'd so great a conquest by his might.

1 The knight himself even trembled at his fall, 2 So huge and horrible a mass it seemed; 3 And his dear lady, that beheld it all, 4 Dared not approach for dread, which she misdeemed,

misdeemed > [had conceived through misjudgement]

5 But yet at last, when the direful fiend

direful > terrible, dreadful