What is the meaning of rat?

noun

• Any of various long-tailed rodents similar to but larger than a mouse.
• Someone who works (or provides workers) during a strike.
  • synonyms: scab, strikebreaker, blackleg
• A person who is deemed to be despicable or contemptible.
  • usage: "only a rotter would do that"; "kill the rat"; "throw the bum out"; "you cowardly little pukes"; "the British call a contemptible person a `git'"
  • synonyms: rotter, dirty dog, skunk, stinker, stinkpot, bum, puke, crumb, lowlife, scum bag, so-and-so, git
• One who reveals confidential information in return for money.
  • synonyms: informer, betrayer, squealer, blabber
• A pad (usually made of hair) worn as part of a woman's coiffure.

verb

• Desert one's party or group of friends, for example, for one's personal advantage.
• Employ scabs or strike breakers in.
• Take the place of work of someone on strike.
  • synonyms: fink, scab, blackleg
• Give (hair) the appearance of being fuller by using a rat.
• Catch rats, especially with dogs.
• Give away information about somebody.
  • usage: "He told on his classmate who had cheated on the exam"
  • synonyms: denounce, tell on, betray, give away, grass, shit, shop, snitch, stag