3 And often bounding on the bruised grass, 4 As for great joyance of his new-come guest.
As > [As though] joyance of > delight in; hence: delight in the arrival of
5 Eftsoons he gan advance his haughty crest,
Eftsoons > Thereupon gan > did haughty > arrogant; high, imposing
6 As chafed boar his bristles does uprear,
chafed > enraged; fretting
7 And shook his scales to battle ready dressed;
dressed > arrayed
8 That made the Redcross Knight nigh quake for fear, 9 As bidding bold defiance to his foeman near.
bidding > offering, proclaiming, threatening foeman > foe, enemy, enemy in war