aggressor vs assailant

aggressor and assailant both are nouns.

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

As nouns, aggressor and assailant are synonyms defined as:

Other synonyms of aggressor include assaulter, attacker.

aggressor (noun)	assailant (noun)
someone who attacks	someone who attacks
a confident assertive person who acts as instigator