1 Whom when the good Sir Guyon did behold, 2 His heart gan wax as stark as marble stone,
gan > did; began to wax > grow stark > rigid, incapable of movement
3 And his fresh blood did freeze with fearful cold, 4 That all his senses seemed bereft at one:
That > [So that] at one > at once, simultaneously
5 At last his mighty ghost began deep to groan,
ghost > spirit
6 As lion, grudging in his great disdain,
grudging > murmuring, grumbling; hence: growling disdain > indignation, anger
7 Mourns inwardly, and makes to himself moan; 8 Till ruth and frail affection did constrain
ruth > pity