1922, American English, perhaps 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 1968 (also in 1961 variant skyjack), extended 1970s to any form of public transportation. Related: Hijacked; hijacking.[hijack etymology, hijack origin, 英语词源]