hijacking vs robbery

hijacking and robbery both are nouns.

Word	Noun	Adjective	Verb	Adverb
hijacking	Yes	No	No	No
robbery	Yes	No	No	No

As nouns, robbery is a hypernym of hijacking; that is, robbery is a word with a broader meaning than hijacking:

hijacking: robbery of a traveller or vehicle in transit or seizing control of a vehicle by the use of force
robbery: larceny by threat of violence

hijacking (noun)	robbery (noun)
robbery of a traveller or vehicle in transit or seizing control of a vehicle by the use of force	larceny by threat of violence
	plundering during riots or in wartime