<p><strong>Verb</strong></p><ul><li>(used with or without object)<ul><li>to hit hard, especially on the head.</li><li>clonk (def 2).</li></ul></li></ul><p><strong>Noun</strong></p><ul><li>a hard hit, especially on the head.</li><li>Informal: a stupid person; clunkhead.</li><li>clonk (def 1).</li><li>Informal: clunker (def 2).</li></ul>