Meaning

• A medium-sized rodent belonging to the genus Rattus.

• Any of the numerous members of several rodent families (e.g. voles and mice) that resemble true rats in appearance, usually having a pointy snout, a long, bare tail, and body length greater than about 12 cm, or 5 inches.

• A person who is known for betrayal; a scoundrel; a quisling.

  "What a rat, leaving us stranded here!"

• An informant or snitch.

• A scab: a worker who acts against trade union policies.

• A person who routinely spends time at a particular location.

  "He loved hockey and was a devoted rink rat."

• A wad of shed hair used as part of a hairstyle.

• A roll of material used to puff out the hair, which is turned over it.

• Vagina.

  "Get your rat out."

• Short for muskrat.

Meaning

• (usually with “on” or “out”) To betray a person or party, especially by telling their secret to an authority or an enemy; to turn someone in.

  "He is going to rat us out!"

• To work as a scab, going against trade union policies.

• (of a dog, etc.) To kill rats.