mischievous > {Producing or intending harm} intent > purpose, intention
3 Now that he had her singled from the crew 4 Of courteous knights, the prince and Faery gent,
gent > noble
5 Whom late in chase of beauty excellent
late > recently (see 301.18-19) chase > pursuit
6 She left, pursuing that same foster strong;
foster > forester
7 Of whose foul outrage they impatient,
impatient > [being] intolerant
8 And full of fiery zeal, him followed long, 9 To rescue her from shame, and to revenge her wrong.