<p><strong>Noun</strong></p><ul><li>Any of several long-tailed rodents of the family Muridae, of the genus Rattus and related genera, distinguished from the mouse by being larger.</li><li>Any of various mammals similar to or related to the long-tailed rodents of the genus Rattus.</li><li>A scoundrel.</li><li>A person who abandons or betrays their party or associates, especially in a time of trouble.</li><li>An informer.</li><li>A scab laborer.</li><li>A person who frequents a specified place: gym rats.</li><li>A mall rat; gym rats.</li><li>A pad with tapered ends formerly used in women's hairstyles to give the appearance of greater thickness.</li></ul><p><strong>Interjection</strong></p><ul><li>Rats, slang. (An exclamation of disappointment, disgust, or disbelief.)</li></ul><p><strong>Verb</strong></p><ul><li>(Used without object) to desert one's party or associates, especially in a time of trouble.</li><li>To turn informer; squeal: He ratted on the gang, and the police arrested them.</li><li>To work as a scab.</li><li>To hunt or catch rats.</li><li>(Used with object) to make (the hair) appear thicker by use of a small pad of material or by teasing.</li></ul><p><strong>Verb Phrase</strong></p><ul><li>(Slang) to inform on: He ratted out his partners in exchange for a lighter sentence.</li></ul>