Final answer:
Paul Revere used the term 'massacre' to describe the event because the engraving he circulated depicted the British soldiers firing ruthlessly into a crowd of unarmed, fleeing civilians.
Step-by-step explanation:
Paul Revere used the term 'massacre' to describe the event because the engraving he circulated depicted the British soldiers firing ruthlessly into a crowd of unarmed, fleeing civilians. This engraving, which was based on an image by engraver Henry Pelham, portrayed the British as the aggressors and the colonists as the innocent victims.