2 Does overspread his long brass-scaly back, 3 Whose wreathed boughts whenever he unfolds,
boughts > coils
4 And thick entangled knots adown does slack,
adown > down
5 Bespotted as with shields of red and black,
Bespotted > {Spotted all over; the prefix is intensive}
6 It sweeps all the land behind him far, 7 And of three furlongs does but little lack;
furlong > {An eighth of a mile, 220 yards, about 201 metres}
8 And at the point two stings infixed are, 9 Both deadly sharp, that sharpest steel exceed far.