Yes, rat is a Scrabble word!

Verb

1. Desert one's party or group of friends, for example, for one's personal advantage

2. Employ scabs or strike breakers in

3. Take the place of work of someone on strike

4. Give (hair) the appearance of being fuller by using a rat

5. Catch rats, especially with dogs

6. Give away information about somebody

Noun

1. Any of various long-tailed rodents similar to but larger than a mouse

2. Someone who works (or provides workers) during a strike

3. A person who is deemed to be despicable or contemptible

4. One who reveals confidential information in return for money

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