highwayman vs highjacker

highwayman and highjacker both are nouns.

Word	Noun	Adjective	Verb	Adverb
highwayman	Yes	No	No	No
highjacker	Yes	No	No	No

As nouns, highwayman and highjacker are synonyms defined as:

highwayman and highjacker: a holdup man who stops a vehicle and steals from it

Other synonyms of highwayman include hijacker, road agent.

highwayman (noun)	highjacker (noun)
a holdup man who stops a vehicle and steals from it	a holdup man who stops a vehicle and steals from it
	someone who uses force to take over a vehicle (especially an airplane) in order to reach an alternative destination