rat (Noun) — Any of various long-tailed rodents similar to but larger than a mouse.
rat (Noun) — Someone who works (or provides workers) during a strike.
rat (Noun) — A person who is deemed to be despicable or contemptible. ex. "kill the rat"
rat (Noun) — One who reveals confidential information to the police or other authority. ex. "The mafia liquidated the rat"
rat (Noun) — A pad (usually made of hair) worn as part of a woman's coiffure.
rat (Noun) — Someone who reports another person's wrongdoings to someone in authority.
rat (Verb) — Desert one's party or group of friends, for example, for one's personal advantage.
rat (Verb) — (industry) employ scabs or strike breakers in.
rat (Verb) — Take the place of work of someone on strike.
rat (Verb) — Give (hair) the appearance of being fuller by using a rat.
rat (Verb) — Catch rats, especially with dogs.
rat (Verb) — Give away information about somebody.