<p><strong>Interjection</strong></p><ul><li>(used to express contempt or disapprobation or to startle or frighten.)</li></ul><p><strong>Noun</strong></p><ul><li>boo (plural: boos).</li><li>an exclamation of contempt or disapproval: a loud boo from the bleachers.</li></ul><p><strong>Verb</strong></p><ul><li>(used without object) booed, booing.</li><li>to cry boo in derision.</li><li>(used with object) booed, booing.</li><li>to show disapproval of by booing.</li></ul>