Bellicosity is the noun for being bellicose: the quality of seeming likely to start a fight or an argument. If a speech is bellicose, you can talk about the bellicosity of the speech. It is even more formal and even rarer than bellicose. You will meet it in news analysis and history writing, almost never in a shop or a classroom chat. Everyday English would say aggressiveness, a warlike tone, or just “they sounded so ready for a fight.” The tidy dictionary line often repeats the adjective’s meaning (“behaving in a way that is likely to start a fight”); though actually, this word names the quality or the atmosphere, not a single action. Same warning as bellicose: no bells.

好戰、好鬥的態度（極書面；bellicose 的名詞）