pirate vs skyjack

pirate is a noun but skyjack is not a noun.

Word	Noun	Adjective	Verb	Adverb
pirate	Yes	No	Yes	No
skyjack	No	No	Yes	No

As verbs, skyjack is a hyponym of pirate; that is, skyjack is a word with a more specific, narrower meaning than pirate:

Other hyponyms of pirate include carjack.

pirate (noun)	skyjack (noun)
a ship that is manned by pirates
someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation
someone who uses another person's words or ideas as if they were his own

pirate (verb)	skyjack (verb)
take arbitrarily or by force	subject an aircraft to air piracy
copy illegally; of published material