If you are dismissive, you will not take someone or something seriously. You treat the idea, the worry, or the person as small — not worth a real look. It is more than “I don’t agree.” You are pushing it away, often with a short answer, a bored voice, or a look that says this is nothing. People use it about a tone, a comment, or a whole way of treating someone. It is a slightly formal, adult word; children feel this all the time but rarely name it. Though actually, in real talk we more often show it than say the word: a shrug, “whatever,” changing the subject. Calling someone dismissive is itself a bit sharp — you are judging how they treated another person.