2 But, rudely rending up his helmet, would
rudely > roughly would > [he would]
3 Have slain him straight: but when he sees his age,
straight > straightway, immediately
4 And hoary head of Archimago old, 5 His hasty hand he does amazed hold, 6 And half ashamed, wondered at the sight:
wondered > marvelled
7 For that old man well knew he, though untold,
untold > [without needing to be told]
8 In charms and magic to have wondrous might, 9 Neither ever wont in field, nor in round lists, to fight.
wont > accustomed field > battle round lists > enclosures for tourneys ("lists" were the palisades enclosing the tilting-ground)