Hello. You did not enter the sentence that this question refers to, which makes it impossible for me to answer it accurately, but stop helping, I will show you the possible meanings that the word "cavalier" can have. Thus, you can reread the sentence where that word is inserted, replacing it with the meanings and seeing which of the meanings allows the sentence to make sense.
The word "cavalier" can take on the meaning of "knight," that is, a soldier who exercises his duties on a horse. In addition, you can refer to a man with courteous and charming behavior, just as you can refer to an arrogant, mannerless, ignorant and brute person.