nightrider vs aggressor

nightrider and aggressor both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightrider	Yes	No	No	No
aggressor	Yes	No	No	No

As nouns, aggressor is a hypernym of nightrider; that is, aggressor is a word with a broader meaning than nightrider:

nightrider: member of a secret mounted band in United States South after the American Civil War; committed acts of intimidation and revenge
aggressor: someone who attacks

Other hypernyms of nightrider include assailant, assaulter, attacker.

nightrider (noun)	aggressor (noun)
member of a secret mounted band in United States South after the American Civil War; committed acts of intimidation and revenge	someone who attacks
	a confident assertive person who acts as instigator