noun
plural rats
[count] a small animal that has a pointed nose and a long, thin tail
informal
a person who is not loyal or who cannot be trusted
a person who is bad or cruel
US informal :a person who spends a lot of time in a specified place
smell a rat
informal :to think or suspect that something is wrong about a situation
verb
rats; ratted; ratting
informal :to tell someone in authority (such as the police) about something wrong that someone has done :to betray someone [no obj]