A person who unlawfully takes someone away against their will, usually for ransom.
From 'kid' (child, from Scandinavian origin) plus 'napper' (one who naps/steals). The term emerged in the 17th century when child abduction for servitude became a crime.
The word 'kidnapper' was literally invented for criminals who stole kids to sell them as servants—it shows how English creates new words for new crimes, and this one stuck because the crime unfortunately became common.
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