<p><strong>Verb</strong></p><ul><li>to act in response to an agent or influence</li><li>to act reciprocally upon each other, as two things</li><li>to act in a reverse direction or manner, especially so as to return to a prior condition</li><li>to act in opposition, as against some force</li><li>to respond to a stimulus in a particular manner</li><li>to undergo a chemical reaction</li></ul>