A useful reference for etymology can be found here at http://www.etymonline.com/index.html.

hijack - 1923, Amer.Eng., from high(way) + jacker "one who holds up." Originally "to rob (a bootlegger, smuggler, etc.) in transit;" sense of "seizing an aircraft in flight" is 1960s (also in 1961 variant skyjack), extended 1970s to any form of public transportation.


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