harasser vs attacker

harasser and attacker both are nouns.

Word	Noun	Adjective	Verb	Adverb
harasser	Yes	No	No	No
attacker	Yes	No	No	No

As nouns, attacker is a hypernym of harasser; that is, attacker is a word with a broader meaning than harasser:

Other hypernyms of harasser include aggressor, assailant, assaulter.

harasser (noun)	attacker (noun)
a persistent attacker	someone who attacks
a persistent tormentor