paynim > pagan, heathen
2 And full of wrath, that, with his sharp-head spear, 3 Through vainly crossed shield he quite did pierce;
vainly crossed > (Because its cross is counterfeit)
4 And, had his staggering steed not shrunk for fear, 5 Through shield and body eke he should him bear:
eke > also; hence: both bear > [have] thrust
6 Yet so great was the puissance of his push,
puissance > power
7 That from his saddle quite he did him bear:
bear > carry
8 He tumbling rudely down to ground did rush,