That > [So that]
4 As in great muse, nor word to creature spoke.
muse > {Abstraction; the action of musing}
5 At last his solemn silence thus he broke, 6 With doubtful eyes fast fixed on his guest:
fast > firmly
7 "Redoubted knight, that for my only sake
Redoubted > Distinguished; feared; dreaded
8 Your life and honour late adventured,
adventured > risked
9 Let naught be hidden from me, that ought to be expressed.