hijack vs usurp

hijack is a noun but usurp is not a noun.

Word	Noun	Adjective	Verb	Adverb
hijack	Yes	No	Yes	No
usurp	No	No	Yes	No

As verbs, usurp is a hypernym of hijack; that is, usurp is a word with a broader meaning than hijack:

hijack: seize control of
usurp: seize and take control without authority and possibly with force; take as one's right or possession

Other hypernyms of hijack include arrogate, assume, seize, take over.

hijack (noun)	usurp (noun)
seizure of a vehicle in transit either to rob it or divert it to an alternate destination

hijack (verb)	usurp (verb)
take arbitrarily or by force	seize and take control without authority and possibly with force; take as one's right or possession
seize control of	take the place of