When you're interviewing someone, their effusiveness makes them a great subject — they have so many interesting things to say — although it can be hard for you to get a word in edgewise. In a typical preschool classroom, there are kids who are quiet and shy, and others whose effusiveness leads them to talk incessantly. This noun comes from the related adjective, effusive, "flowing profusely," from the Latin effundere, "to pour forth or spread abroad."