Unwares > Unexpectedly (on the part of Britomart); suddenly
5 That little drops empurpled her fair breast.
That > [So that] empurpled > reddened
6 Exceeding wroth therewith the virgin grew,
therewith > with that; thereupon
7 Albe the wound were nothing deep impressed,
Albe > Although nothing deep > not at all deeply
8 And fiercely forth her mortal blade she drew,
mortal > lethal
9 To give him the reward for such vile outrage due.