RAT

noun

1. A medium-sized rodent belonging to the genus Rattus.
2. 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.
3. A person who is known for betrayal; a scoundrel; a quisling.

verb

1. (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.
2. To work as a scab, going against trade union policies.
3. (of a dog, etc.) To kill rats.