harassment vs mistreatment

harassment and mistreatment both are nouns.

Word	Noun	Adjective	Verb	Adverb
harassment	Yes	No	No	No
mistreatment	Yes	No	No	No

As nouns, mistreatment is a hypernym of harassment; that is, mistreatment is a word with a broader meaning than harassment:

harassment: the act of tormenting by continued persistent attacks and criticism
mistreatment: the practice of treating (someone or something) badly

harassment (noun)	mistreatment (noun)
the act of tormenting by continued persistent attacks and criticism	the practice of treating (someone or something) badly
a feeling of intense annoyance caused by being tormented