HISSING (5 letters) Verbal disapproval is a form of communication that expresses disapproval or criticism without using words. It can be expressed in a variety of ways, such as booing and HISSING. Booing is a loud, harsh sound made by a group of people to show their disapproval or dissatisfaction with something. HISSING is a sound made by forcing air through the lips to express disapproval or contempt. Both of these forms of verbal disapproval are used to express dissatisfaction or disapproval of a person, situation, or event.