Middle English (originally denoting a heretic, specifically an Albigensian): from Middle Dutch, from Old French bougre ‘heretic’, from medieval Latin Bulgarus ‘Bulgarian’, particularly one belonging to the Orthodox Church and therefore regarded as a heretic by the Roman Church.
The sense ‘sodomite’ (16th century) arose from an association of heresy with forbidden sexual practices; its use as a general insult dates from the early 18th century.
