stour > conflict, combat
4 Of his fierce foe, him to a tree applies,
him > [himself, the lion] applies > places in contact; hence: backs up against; also: directs his path, makes his way
5 And when him running in full course he spies,
him > [the unicorn]
6 He slips aside; while that furious beast 7 His precious horn, sought of his enemies,
precious > (Because it was believed to have medicinal or magical properties, esp. as an antidote to or preventive of poison)
8 Strikes in the stock, nor thence can be released,
stock > trunk
9 But to the mighty victor yields a bounteous feast.