brute vs aggressor

brute and aggressor both are nouns.

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

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

Other hypernyms of brute include assailant, assaulter, attacker.

brute (noun)	aggressor (noun)
a living organism characterized by voluntary movement	someone who attacks
a cruelly rapacious person	a confident assertive person who acts as instigator

brute (adjective)	aggressor (adjective)
resembling a beast; showing lack of human sensibility