What is rat?
rat: desert one's party or group of friends, for example, for one's personal advantage; employ scabs or strike breakers in; take the place of work of someone on strike; give (hair) the appearance of being fuller by using a rat; catch rats, especially with dogs; give away information about somebody
Updated on Saturday, February 04 2012 at 04:14AM EST
Source:
wordnetweb.princeton.edu/...