ebon > {Ebony, made of ebony, a tree of the family Ebenaceae, esp. Diospyros ebenus, producing hard black wood}
3 Whose harmful head, thrice heated in the fire, 4 Had rived many a breast with pikehead square;
rived > split pikehead > [the point of the spear] square > [Perhaps meaning square in cross-section; also: direct, straight, just, honourable; and adv. senses]
5 A goodly person, and could manege fair
goodly > {Well-favoured, of good appearance} manege > manage, control (a term in horsemanship)
6 His stubborn steed with curbed canon bit,
curbed > {Having a chain or strap passing under the lower jaw, fastened to the upper ends of the branches of the bit: used for controlling an unruly horse} canon bit > {A mild, uncruel bit}
7 Who under him did trample as the air, 8 And chafed that any on his back should sit; 9 The iron rowels into frothy foam he bit.
rowels > {Knobs on the bit}
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