Definition of: rat

(rat) noun
1. A destructive and injurious rodent (family Muridae) of world–wide distribution, larger and more aggressive than the mouse; especially, the Norway rat (Rattus norvegicus) and the smaller roof or black rat (R. rattus): both are carriers of the plague bacillus transmitted by the rat flea.
2. Some other mammal like or likened to the rat.
3. Slang A cowardly or selfish person who deserts or betrays his associates.
4. A slender cushion of curled hair or the like, worn by women, with the natural hair rolled over it.
—v.i. rat·ted, rat·ting
1. To hunt rats.
2. Slang To desert one's party, companions, etc., especially for one's own safety or advantage.
3. Slang To inform; act the betrayer. [OE ræt]