rat

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various long-tailed rodents resembling mice but larger, especially one of the genus Rattus.
• noun Any of various animals similar to one of these long-tailed rodents.
• noun A despicable person, especially one who betrays or informs upon associates.
• noun A scab laborer.
• noun A pad of material, typically hair, worn as part of a woman's coiffure to puff out her own hair.
• noun Slang A person who frequently passes time at a particular place. Often used in combination.
• intransitive verb To hunt for or catch rats, especially with the aid of dogs.
• intransitive verb Slang To reveal incriminating or embarrassing information about someone, especially to a person in authority.
• intransitive verb Slang To work as a scab laborer.
• intransitive verb To puff out (the hair) with or as if with a pad of material.

from The Century Dictionary.

• noun plural An exclamation used to indicate incredulity or ironical disagreement with a statement; humbug.
• noun A rodent of some of the larger species of the genus Mus, as M. rattus, the black rat, and M. decumanus, the gray, brown, or Norway rat: distinguished from mouse.
• noun Any rodent of the family Muridæ; a murine; in the plural, the Muridæ.
• noun Any rodent of the suborder Myomorpha.
• noun Some other rodent, or some insectivore, marsupial, or other animal like or likened to a rat.
• noun A person who is considered to act in some respect in a manner characteristic of rats: so called in opprobrium.
• noun A workman who accepts lower wages than those current at the time and place or required by an authorized scale, or one who takes a position vacated by a striker, or one who refuses to strike when others do.
• noun A clergyman: so called in contempt.
• noun Something suggesting the idea of a rat, as a curving roll of stuffed cloth or of crimped hair-work, with tapering ends, formerly (about 1860–70) and still occasionally used by women to puff out the hair, which was turned over it.
• noun Same as bandicoot, 2.
• noun A rag; tatter.
• To tear.
• A term of objurgation, used in the imperative.
• To catch or kill rats; follow the business of a ratter or rat-catcher.
• To go over from one party or cause to another, especially from a party or cause that is losing or likely to lose, as rats run from a falling house; desert one's party or associates for advantage or gain; become a renegade.
• To work for less than current wages, to refuse to strike with fellow-workmen, or to take the place of one who has struck: often with indefinite it. See rat, n., 5 .
• To puff out (the hair) by means of a rat. See rat, n., 6.
• To displace or supplant union workers in: as. to rat an office or a shop.
• A Middle English contracted form of redeth, the third person singular present indicative of read.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb In English politics, to desert one's party from interested motives; to forsake one's associates for one's own advantage; in the trades, to work for less wages, or on other conditions, than those established by a trades union.
• intransitive verb To catch or kill rats.
• intransitive verb To be an informer (against an associate); to inform (on an associate); to squeal; -- used commonly in the phrase to rat on.
• noun (Zoöl.) One of several species of small rodents of the genus Rattus (formerly included in Mus) and allied genera, of the family Muridae, distinguished from mice primarily by being larger. They infest houses, stores, and ships, especially the Norway rat, also called brown rat, (Rattus norvegicus formerly Mus decumanus), the black rat (Rattus rattus formerly Mus rattus), and the roof rat (formerly Mus Alexandrinus, now included in Rattus rattus). These were introduced into America from the Old World. The white rat used most commonly in laboratories is primarily a strain derived from Rattus rattus.
• noun Local, U.S. A round and tapering mass of hair, or similar material, used by women to support the puffs and rolls of their natural hair.
• noun Cant One who deserts his party or associates; hence, in the trades, one who works for lower wages than those prescribed by a trades union.
• noun (Zoöl.) any Indian rodent of the genus Rhizomys.
• noun (Zoöl.) See under Beaver and Coast.
• noun (Zoöl.) the mole rat.
• noun (Zoöl.) a long-haired rat (Sigmodon hispidus), native of the Southern United States and Mexico. It makes its nest of cotton and is often injurious to the crop.
• noun See Ground Pig, under Ground.
• noun See under Hedgehog.
• noun (Zoöl.) the potoroo.
• noun (Zoöl.) the common brown rat. See Rat.
• noun (Zoöl.) Any African rodent of the genus Cricetomys.
• noun (Ethnol.) a tribe of Indians dwelling near Fort Ukon, Alaska. They belong to the Athabascan stock.
• noun (Zoöl.) See Mole rat, under Mole.