privy spials > hidden spies

4 To weet what course he takes, and how he fares;

weet > find out

5 To catch him at a vantage in his snares.

vantage > advantage

6 But now so wise and wary was the knight 7 By trial of his former harms and cares, 8 That he descried, and shunned still, his sleight:

still > constantly his sleight > [Archimago's] cunning, trickery

9 The fish that once was caught, new bait will hardly bite.

201.5

Nath'lesse th'Enchaunter would not spare his paine,
2 In hope to win occasion to his will;
Which when he long awaited had in vaine,
4 He chaungd his minde from one to other ill:
For to all good he enimy was still.
6 Vpon the way him fortuned to meet,
Faire marching vnderneath a shady hill,
8 A goodly knight, all armd in harnesse meete,
That from his head no place appeared to his feete.