shroud > shelter; conceal
3 Yet fear them follows still, whereso they be,
still > continually whereso > wherever
4 Each trembling leaf and whistling wind they hear 5 As ghastly bug their hair on end does rear:
As > [Like a] ghastly > {Ghostly; causing terror of the supernatural} bug > {Bugbear, bogy, object of needless dread}
6 Yet both do strive their fearfulness to feign.
feign > conceal (SUS; cf. 112.10:1)
7 At last they heard a horn, that shrilled clear 8 Throughout the wood, that echoed again, 9 And made the forest ring, as it would rive in twain.
it would rive > [if it would split it] twain > two
203.21