rat

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!"

(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.