質問: kidnappingを成人にも使う理由か由来は 題の通りです。
回答: good question! the word dates back 400-odd years, incorporating the word "napper" meaning a thief. it was originally applied to the process of stealing children and carrying them off to work as slaves on the american plantations. the nappers who did this might also occasionally be able to overcome a weak adult as well as a child for that purpose, but because that did not happen very often no separate word came into being for stealing an adult. so "kidnapping" has stuck as meaning carrying off a child or an adult. https://answers.yahoo.com/question/index?qid=20101018232721aahaknv