A person who holds beliefs that contradict the official teachings of a religion, or someone who rejects widely accepted ideas.
From Greek 'hairetikos' (able to choose), from 'hairesis' (choice, sect). Originally meant someone who chose their own beliefs rather than accepting doctrine; the negative sense developed as institutions gained power to define 'correct' belief.
Many people we now consider geniuses—like Galileo—were called heretics by powerful institutions; it's a reminder that 'wrong' beliefs today might be tomorrow's accepted truth.
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