rat

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various long-tailed rodents resembling mice but larger, especially one of the genus Rattus.
2. n. Any of various animals similar to one of these long-tailed rodents.
3. n. Slang A despicable person, especially one who betrays or informs upon associates.
4. n. Slang A scab laborer.
5. n. A pad of material, typically hair, worn as part of a woman's coiffure to puff out her own hair.
6. v. To hunt for or catch rats, especially with the aid of dogs.
7. v. Slang To betray one's associates by giving information: ratted on his best friend to the police.
8. v. Slang To work as a scab laborer.
9. v. To puff out (the hair) with or as if with a pad of material.

Century Dictionary and Cyclopedia

1. n. 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. The distinction between rat and mouse, in the application of the names to animals everywhere parasitic with man, is obvious and familiar. But these are simply larger and smaller species of the same genus, very closely related zoölogically, and in the application of the two names to the many other species of the same genus all distinction between them is lost.
2. n. Any rodent of the family Muridæ; a murine; in the plural, the Muridæ. In this sense, rat includes mouse. American rats or mice are a particular section of the subfamily Murinæ, called Sigmodontes, conflned to America, where no other Murinæ are indigenous. Field-rats, water-rats, meadow-mice, or voles are Muridæ of the subfamily Arvicolinæ. See cuts under Arvicola, Muridæ, muskrat, Neotoma, Nesokia, and Nesomys.
3. n. Any rodent of the suborder Myomorpha. Different animals of several families as Dipodidæ, Zapodidæ, Saccomyidæ, Geomyidæ, Spalacidæ, are often known as rats of some kind distinguished by qualifying words or compound names. See cut under mole-rat.
4. n. Some other rodent, or some insectivore, marsupial, or other animal like or likened to a rat. Thus, among hystricomorphic rodents, many species of Octodontidæ are called rats: as, the spiny rats of the subfamily Echinomyinæ. Some large aquatic shrews are known as muskrats. (See Myogale.) Some rat-like marsupials are known as kangaroo-rats. (See bettong, and cuts under kangaroo-rat and Echimys.)
5. n. A person who is considered to act in some respect in a manner characteristic of rats: so called in opprobrium. Specifically— A man who deserts a party or an association of any kind for one opposed to it in order to gain some personal advantage or benefit; a self-seeking turncoat; a renegade.
6. n. 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.
7. n. A clergyman: so called in contempt.
8. n. 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.
9. n. Same as bandicoot, 2.
10. To catch or kill rats; follow the business of a ratter or rat-catcher.
11. 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.
12. 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 .
13. To puff out (the hair) by means of a rat. See rat, n., 6.
14. To displace or supplant union workers in: as. to rat an office or a shop.
15. n. A rag; tatter.
16. To tear.
17. A term of objurgation, used in the imperative.
18. A Middle English contracted form of redeth, the third person singular present indicative of read.
19. n. plural An exclamation used to indicate incredulity or ironical disagreement with a statement; humbug.

Wiktionary

1. n. zoology A medium-sized rodent belonging to the genus Rattus.
2. n. informal A term indiscriminately applied to numerous members of several rodent families (e.g. voles and mice) having bodies longer than about 12 cm, or 5 inches.
3. n. informal A person who is known for betrayal; a scoundrel; a quisling.
4. n. informal An informant or snitch.
5. n. slang A person who routinely spends time at a particular location.
6. n. Scab.
7. n. London, slang North West London slang term for a vagina.
8. n. A wad of shed hair used as part of a hairstyle.
9. v. usually with “on” or “out” To betray someone and tell their secret to an authority or an enemy; to turn someone in, bewray.
10. v. of a dog, etc. To kill rats.

GNU Webster's 1913

1. n. (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.
2. n. 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.
3. n. 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.
4. v. 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.
5. v. To catch or kill rats.
6. v. To be an informer (against an associate); to inform (on an associate); to squeal; -- used commonly in the phrase to rat on.

WordNet 3.0

1. v. catch rats, especially with dogs
2. v. take the place of work of someone on strike
3. v. desert one's party or group of friends, for example, for one's personal advantage
4. v. employ scabs or strike breakers in
5. n. someone who works (or provides workers) during a strike
6. n. any of various long-tailed rodents similar to but larger than a mouse
7. v. give (hair) the appearance of being fuller by using a rat
8. v. give away information about somebody
9. n. a pad (usually made of hair) worn as part of a woman's coiffure
10. n. a person who is deemed to be despicable or contemptible
11. n. one who reveals confidential information in return for money