puissance > force, power
2 Against that castle restless siege did lay, 3 And evermore their hideous ordinance
hideous > immense, terrific; odious ordinance > battle-array; or, more probably: ordnance, artillery (cf. 211.10:9, 211.12:1)
4 Upon the bulwarks cruelly did play, 5 That now it began to threaten near decay:
That > [So that] decay > downfall, destruction; death
6 And evermore their wicked captain 7 Provoked them the breaches to assay,
assay > assault; attempt
8 Sometimes with threats, sometimes with hope of gain,
hope > promise; expectation
9 Which by the ransack of that piece they should attain.