to seize control of (a vehicle or aircraft) by force while it is in transit
to steal, rob, or kidnap (something or somebody) as if by hijacking
hijacker noun
origin unknown. This word first achieved wide currency in the USA in the 1920s, when it was applied to stealing bootleg alcohol in transit, but there is some evidence that it was earlier used by hoboes to mean ‘to rob a sleeping person’. It has been conjectured that the word derives from High, Jack!, i.e. a command to the victim to put his hands up, or possibly from Hi, Jack!, i.e. a menacing greeting to the victim, but neither explanation is very convincing