Nosiness is the habit of wanting to know things that do not concern you, especially other people’s private affairs. It is the noun for what a nosy person shows. You can talk about “her nosiness”, or someone can apologise for it: “forgive my nosiness”. The noun is a little heavier than the adjective, more like naming the fault. Informal, slightly disapproving, everyday. It is not a crime and not always unkind; some nosiness is just curiosity that has forgotten the line. The kinder word for the same area is curiosity; nosiness is curiosity that has walked into someone else’s business.