by 1922 (perhaps c. 1918), American English, of unknown origin; perhaps from high(way) + jacker "one who holds up" (agent noun from jack (v.)). In early use "to rob (a bootlegger, smuggler, etc.) in transit;" sense of "seize an aircraft in flight" is 1968 (also in 1961 variant skyjack), extended 1970s to any form of public transportation. Related: Hijacked; hijacking. Related: Hijacker.