rat

any of various long-tailed rodents similar to but larger than a mouse

a pad (usually made of hair) worn as part of a woman's coiffure

one who reveals confidential information in return for money

a person who is deemed to be despicable or contemptible

only a rotter would do that

kill the rat

someone who works (or provides workers) during a strike

give away information about somebody

He told on his classmate who had cheated on the exam

catch rats, especially with dogs

give (hair) the appearance of being fuller by using a rat

take the place of work of someone on strike

employ scabs or strike breakers in

desert one's party or group of friends, for example, for one's personal advantage