Other forms: hooted; hooting; hoots
A hoot is the musical call an owl makes. The hoot of an owl sounds very much like the word hoot.
An owl's hoot is the inspiration for a similar sound that people make to show disapproval or scorn: "The sound of the crowd's hoots filled the stadium when the soccer player kicked the ball into his own team's goal." To make this sound, whether you're a person or an owl, is to hoot, and if you don't give a hoot, it means you really don't care at all.