To illegally seize control of a vehicle, aircraft, or ship while it is in transit. The group planned to hijack the plane and demand a ransom.
To take control of something for one's own purposes, often in a forceful or unauthorized manner. The politician tried to hijack the meeting to push his own agenda.
To seize goods from a vehicle in transit by force or intimidation. During Prohibition, bootleggers would often hijack trucks carrying rival shipments of liquor.