Cavalier means showing a casual lack of concern about something important, treating serious matters as if they don't really matter. When a student takes a cavalier attitude toward studying for finals, they act like the tests aren't worth worrying about. When someone is cavalier about safety rules, they ignore warnings that could keep them safe.

The word suggests more than simple carelessness. A cavalier approach combines indifference with a kind of breezy confidence, as if the person thinks they're above the rules or consequences. If your friend borrows your favorite book and treats it in a cavalier way, tossing it around and getting it dirty, they're showing they don't respect something you value.

Today, being cavalier about responsibilities or other people's feelings usually leads to problems, because what you dismiss as unimportant can matter quite a bit to someone else.