<p><strong>Noun</strong></p><ul><li>Any small, wingless insect of the order Anoplura sucking louse, parasitic on humans and other mammals and having mouthparts adapted for sucking, as <em>Pediculus humanus humanus</em> (body louse) or <em>Pediculus humanus capitis</em> (head louse) and <em>Phthirius pubis</em> (crab louse or pubic louse).</li><li>Any insect of the order Mallophaga (bird louse, biting louse, or chewing louse), parasitic on birds and mammals, having mouthparts adapted for biting.</li><li>Plant louse.</li><li>Slang. A contemptible person, especially an unethical one.</li></ul><p><strong>Verb</strong></p><ul><li>(used with object) To delouse.</li></ul><p><strong>Verb Phrase</strong></p><ul><li>Slang. To spoil; botch: Miscasting loused up the movie.</li></ul>