belligerent vs aggressive

belligerent is a noun but aggressive is not a noun.

Word	Noun	Adjective	Verb	Adverb
belligerent	Yes	Yes	No	No
aggressive	No	Yes	No	No

As adjectives, belligerent and aggressive are synonyms defined as:

belligerent and aggressive: characteristic of an enemy or one eager to fight

belligerent (noun)	aggressive (noun)
someone who fights (or is fighting)

belligerent (adjective)	aggressive (adjective)
characteristic of an enemy or one eager to fight	having or showing determination and energetic pursuit of your ends
engaged in war	characteristic of an enemy or one eager to fight
	tending to spread quickly