—n. 1. any of several long-tailed rodents of the family Muridae, of the genus Rattus and related genera, distinguished from the mouse by being larger.
2. any of various similar or related animals.
3. Slang.a scoundrel.
4. Slang. a. a person who abandons or betrays his or her party or associates, esp. in a time of trouble.
b. an informer.
c. a scab laborer.
5. Slang.a person who frequents a specified place: mall rat; gym rat. 6. a pad with tapered ends formerly used in women's hair styles to give the appearance of greater thickness.
7. smell a rat, to suspect or surmise treachery; have suspicion: After noting several discrepancies in his client's story, the attorney began to smell a rat.
—interj. rats,Slang.(an exclamation of disappointment, disgust, or disbelief.)
—v.i. 1. Slang. a. to desert one's party or associates, esp. in a time of trouble.
b. to turn informer; squeal: He ratted on the gang, and the police arrested them. c. to work as a scab.
2. to hunt or catch rats.
—v.t. to dress (the hair) with or as if with a rat.