1rat 
/ˈræt/ noun
plural rats /ˈræt/ noun [count] 1 : a small animal that has a pointed nose and a long, thin tail
▪ a dirty old building infested by rats and mice ▪ a lab/laboratory rat [=a rat that is used by scientists for experiments] ▪ He came in from the rain looking like a drowned rat. [=looking very wet and miserable] — see picture at rodent 2 informal a : a person who is not loyal or who cannot be trusted
▪ I can't believe that rat turned us in to the police!
b : a person who is bad or cruel
▪ No one understands why she's with a rat like him. 3 US, informal : a person who spends a lot of time in a specified place
▪ a mall rat ▪ Every night he goes to work out with the other gym rats.
▪ a dirty old building infested by rats and mice ▪ a lab/laboratory rat [=a rat that is used by scientists for experiments] ▪ He came in from the rain looking like a drowned rat. [=looking very wet and miserable] — see picture at rodent
▪ I can't believe that rat turned us in to the police!
b : a person who is bad or cruel
▪ No one understands why she's with a rat like him.
▪ a mall rat ▪ Every night he goes to work out with the other gym rats.
smell a rat
informal : to think or suspect that something is wrong about a situation
▪ She smelled a rat when her husband came home with lipstick on his collar.
▪ She smelled a rat when her husband came home with lipstick on his collar.
